This is a great point. To condense what you said a bit: the dot-com bubble followed the democratization of stock trading (which itself got a technological assist from the internet). Lots of people, myself included, who never bought a stock start using online trading accounts. The housing bubble followed the democratization of home buying. Lots of people who never had bought a house before (or a second or third house) start buying houses.
The question I've been asking for a while now: what's the next great financial innovation that's going to revolutionize access to some market to which average people don't currently have easy access?
Going to offer an answer to my own question: where's the next bubble?
My boring answer has always been: commodities. Yeah, ordinary people can buy and sell precious metals now. But wouldn't it be more convenient if you could just directly buy a nicely packaged product online (with no service premium) that represents whatever arbitrary commodity or commodity future (or whatever it is you trade) you desire? I'm sure this would do wonders for oil prices. All those gold trading services that advertise on cable seem to be a niche example of the phenomenon.
However, I just came across something which may offer a more interesting answer: bitcoin, or more generally, currency. I going by what I was just reading here:
There has been a recent democratization of web- and mobile-applications, has there not? It's super easy for me now to make an site with Rails to do x. Same goes for creating and publishing mobile applications. Anyone can now easily make and sell an iPhone app. When has this ever been possible? This is the current democratization, and I don't think it would be unrealistic to suggest it could lead to a bubble.
The question I've been asking for a while now: what's the next great financial innovation that's going to revolutionize access to some market to which average people don't currently have easy access?
I want to be on the upside of the bubble.