Which companies should we follow closely?
Now, granted that scenario is not a great example as email existed as a standard long before AOL came into existence, but I do think that as the number of users on Facebook/Twitter reach their inevitable peak, those companies, too, will be faced with the need to open the gates on their walled garden.
It's interesting that, thus far, both companies have delayed such a situation from arising by buying-out the other platforms people have been moving too (Instagram, Vine, etc.) and incorporating them ever-more-tightly with the parent platform. At some point, though, I think (hope?) this strategy will prove untenable and open interoperability will once again rule the web.
Call it crazy speculation, but I could foresee a resurgence of RSS/Atom eventually doing to Facebook/Twitter what SMTP/POP/IMAP did to AOL. If you think about it, the only thing that RSS/Atom was ever missing from becoming what Facebook/Twitter are today is a central aggregation point in the cloud. A smart startup that pulls a user's Facebook/Twitter feeds and mixes in any other RSS/Atom, as well as allowing users to post back to Facebook/Twitter/Atom could potentially spell the death of proprietary timelines.
A few years ago I would have said you were crazy. But after the race to replace Google Reader, the failure of Google+, the general sense of malaise that many people have with Facebook, and the political echo chamber and general bot fest that is Twitter, I think there's room for another player here.
 despite, importantly, continuing to use it all the time
 my default working assumption when someone follows me is now that it's a bot
I think natural way social networking would go forward is that there will be a lack of interest in general purpose social networking. These will be eventually replaced by cliques kind of things that are context specific. Basically, social structure would be integrated in most products, inherently. Now that might (or might not) require a centralized social graph.
But saying that RSS/Atom would replace proprietary general purpose networking gives an impression that there would still be interest in a Newsfeed going forward. It also assumes that we are at pinnacle of social networking evolution and all that needs to happen is even distribution of power. I think both statements are false. This is exactly the kind of thinking that drives FOSS products 10 years behind time.
The Web is not a distributed AOL. A distributed AOL would have failed. AOL evolved into Web. There are plenty of examples of distributed protocols being evolved into proprietary one. In fact, look at the usage numbers surging on messaging apps. Compare that to rate of e-mail and SMS.
But we're already in a world where kids today see Facebook as something for their parents. And I know more and more people who (like myself) deleted their Facebook account years ago and don't miss it.
Facebook is headed toward irrelevance. It will probably always hang on like AOL and Yahoo still do. But it won't be the center of the online universe like it has been for so long. We're already on the down side of that hill.
Which is to say that they are irrelevant to a lot of people, particularly "early adopters", but they'll be around and profitable for a long time.
Similarly, IBM was computers for 30 years.
Comparing them to simply the most popular social website for the past 10 years is not really fair. The fact that Facebooks value approaches those other two companies only shows how insane the current bubble is.
I could easily see facebook surviving long into the future in a similar way to IBM -- with a focus that is shifted from what made them big player, but still doing valuable work (and making money) in the tech "sphere".
If you only consider relevant company to be one that is creating a new and disrupt technology as their core product then sure they will have to fight daily not to become irrelevant. However, if you consider relevance to mean something that impacts the daily lives of many people, within the last 30 days they had their first 1B active user day. It's just very hard to displace that many people and so many of them have their lives (and memories) on Facebook in terms of the photos and connections. I am not extremely active on Facebook but having an account just seems like that otherwise missing world directory mixed with a personal life timeline which only increases in value as the years pass.
I don't put too much stock in these types of numbers that companies release themselves. Facebook has long had issues with fake accounts created by bots, and has shown little interest in curbing that practice (since it inflates their numbers.)
Even if I accept the number at face value, I think that reflects mainly Facebook getting some penetration into other countries outside of the US. In the US it has already begun to decline, and while the Facebook "wave" may be at different points in other regions of the world, it is unlikely it will hold on for 10 years in those other countries given the increased relevance of other forms of social networking.
I've got the feeling you underestimate how important this central aggregation point actually is. Imho I'd even say it's the paramount reason Facebook/Twitter are still the top dogs, people are just attracted to the (unique) aggregator which already has the most people.
We've have multiple proprietary competitors, an open standard (XMPP), Google even embraced IM federation at some point but removed it later.
Not because my parents are on it (they are), but because it's not fun.
It used to be fun in high school (4-5 years ago) when you could have semi-private conversations with friends through wall posts, back before every status and picture was gamified by "likes", back before everything you ever posted was pinned like a dead moth on your timeline for everyone to see in perpetuity, back before it turned into a bunch of roosters strutting around, sticking their chests out and seeing who can crow the loudest.
Many of my friends share the same sentiments and are dropping off the Facebook grid in favor of Snapchat/direct messaging (Groupme, Whatsapp)/real-life hanging out.
That said, I don't think Facebook is going anywhere anytime soon:
> Facebook pages/events are essential for businesses and organizations. It's a large inconvenience not to have one if you're a business owner or a college student, especially in countries outside the US with less developed internet infrastructure and resources.
> Huge room for growth internationally. In some nascent markets, people even think that Facebook is the internet. 
> Facebook owns Whatsapp, Instagram, and Oculus Rift. Very strong portfolio of companies with a lot of brilliant people behind them.
Twitter does seem to be gaining in the international recognition, probably still residual effect stemming from the media attention gained by the Arab Spring and other social news events that unfolded on Twitter.
EDIT: Can anyone explain what is causing downvoting? Are anecdotes not valuable information?
That has been working extremely well. The only thing that I miss os the opportunity to go back to arbitrary points in time like I could on the old blog.
I find "social" in social network is a form of social that I am mostly not comfortable with.
There is one the notable exception though - a startup that got enough traction to worry Facebook and then sold to Google might actually come out on top. Google actively wants to compete with Facebook. The problem for such a startup would be Google's track record in social, so they'd need to resist Google's desire to assimilate them too much. That would (probably) be quite hard.
A Facebook competitor faced with an offer from Facebook would not have that problem. It's very likely that the competitor and Facebook would be very well aligned strategically. Selling would mean the competitor would get to where they want to go. Very few founders would say capable of saying no.
So if you mean will other services in that general fuzzy category become popular, the answer is 100% yes. It's happening all the time. Whatsapp, snapshot, whatnot. These pop up all the time and many get traction.
If you mean will Twitter & Facebook loose popularity, that's harder to answer. But, I think it's reasonably likely. They're basically mediums for online culture and online cult evolves fast. It also depends on your horizon. If the question is "will a large portion of humans check Facebook daily in 100 years?" that seems pretty unlikely.
The Internet Of Things IoT will be a precursor to any device being a node in a massive mesh net. That means that I can run my own private, secure personal social node on my cell phone, or even on my toaster.
The front end app will literally just be a front. The backend processing can be done on any number of nano-cloud processing instances run by companies like Amazon or Microsoft.
Storage similarly will be outsourced, but all data will be protected at rest using strong encryption.
One thing we are seeing a bit and may see more of is microplatforms. They will focus on specific interactions instead of the generic type FB goes for (thinking bangwithfriends (some would even say Tinder is this type of SN), sector-specific Linkedin, regional social networks).
FB will be around for a long long while thou. It was a twist of genius implementing federated logins, in effect becoming your passport to the internet.
I still cannot black- or whitelist websites that I want or don't want to show up in my results. Really, I want to control what I see!!!
When another search engine gives me the flexibility to control my results, I'll jump ship. But currently even with annoying results that I don't want to ever see again, google's results are still better than anything else.
- Although yandex is definitely better for search results in Russian.
People are realizing that the benefits of social media are curses in disguise. Instead of a stream of interesting dialog between friends, they have a raging river polluted with the rantings of every person they ever met or any company they ever liked. It's hard to have meaningful interactions with people when that girl you met one night at a friend's party, your crazy uncle, and Starbucks are all screaming in your face.
Just as people are getting sick of Social Networking, businesses are starting to realize that the promise of the Social Network as a way to connect with customers isn't happening.
Case in point, I was shopping online the other day for an office chair and was prompted to take a survey (I'm a sucker for surveys). The survey went something like this...
Will you be sharing anything on our site with social media? No.
Have you ever shared anything on our site with social media? No.
Have you ever shared anything on any of our competitor's sites with social media? No.
Have you ever shared anything from an online store on social media? No.
Do you find any value in social media buttons on online stores? No.
When you are shopping online, do you utilize social media? No.
Mark is smart enough to buy his competition before it bites.
LinkedIn is clearly the worst of these three. Please let an ethical competitor kill them ...
Relying on blockchain technology is needed only when everyone should trust on something, but once you have the peer to peer connection this is no longer needed.
FB (the company) is hedging their bets by acquiring Instagram and Whatsapp and not relying only on Facebook (the platform)