"what will be successful in 25 years, will have to be completely unrelated from what Google is doing now"
I know very little about SEO or website design, but isn't google already kinda tipping their hand to what the future will hold?
Without adblock, a quick google search shows that the entire top half of the result page are ads. To me, it's fairly obvious the future will bring pay-for-priority search inclusion. You want a top spot? Break out your wallet.
Whether that's a good thing or a bad thing, only time will tell. I'm more curious about search engine competitors 25 years from now. Google's had a great decade, but that can't last forever ... can it?
The top half of the results page will be ads if you searched for something so generic that there essentially are no good organic results. Certainly if you search for something specific, it won't be like that.
For instance, I recently watched a terrible movie, and I'm trying to remember what it's called so I can warn people off of it. Searching for that is a specific piece of information, not a generic "noun"-type thing:
Commercial intent is more important than how broad / generic the term is.
A query like "sports" or "news" may or may not have an ad in the search results. Keywords like "credit cards for people with poor credit scores" will almost always show lots of ads, even though the query is quite specific and contains 8 words.
In some particularly valuable verticals (like hotels) Google then further adds their other paid verticals to the results in addition to the AdWords ads.
One of Matt's videos (not sure which one) mentioned online publishers tend to focus a lot on say 10% to 20% of highly commercial terms, while often paying much less attention to the rest of the searches as the commercial terms typically are far more valuable than the informational ones. (Mesothelioma lawyers can afford to pay more for traffic than say people selling flour, or people offering recipes that contain flour).