We unfortunately don't know much about what's coming next, but we do know one thing that's scheduled to show up, at least before the next expansion: some sort of housing. All the Blue hints point to guild housing, but player housing is an idea that's been tossed around as well. There's just one problem to MMO housing, however. As Hardcore Casual points out, it often becomes a ghost town.
Back when I played Dark Age of Camelot, I remember visiting the guild housing area only once (the guild I joined was mostly lowbies, and we never had enough cash to buy property of our own), and it was a strange experience-- acres upon acres of customized buildings, all completely and totally empty as far as I could see. There were a few NPCs around (DAoC had a feature where you could have NPCs stand outside your house to sell your crafts while you were gone), but otherwise it was more like an abandoned trailer park than anything else. As HC says, the "IDEA" of housing is great-- you can have your own place to hang out, show off, and build to your heart's content. But in practice, most players would rather be exploring the world Blizzard designed then stuck in a small room that they made themselves.
Now, the obvious solution for this is instancing, and in fact, Blizzard has already foreseen this-- there are currently instance portals in a few cities that have been rumored to serve as either player or guild housing. If instances were used as housing, we'd just all own the same apartment in Stormwind. But you have to balance that against the other feature of housing-- actually showing it off. Wandering around the houses in DAoC was a kind of (lonely) fun, if only to see what other people had created, and with just an instance, all you'd get to see is the inside. It'll be interesting to see how Blizzard balances player-created content (which can sometimes be boring or ugly), with their own interesting design.