I think all will depend on the way the Internet's gonna go ...
It's thanx to sites like melodicrock.com that many people (including me) have regained contact with / learned about melodic rock/AOR, and I think the same can go for any other genre in music ; everything that's underground will eventually surface through Internet... and thanx to soundbytes you can listen to just about everything that comes out and decide what you like best.
As far as prevailing styles ... I think in the end it'll come to all styles living one next to another, and everybody sticking to whatever he/she likes best.