New warchief is Vol'jin and I think Jaina Proudmore is going to be following Arthas path and will be the next big baddie for the last expansion before WoW 2
There will be 2 more expansions. 90-95 and 95-100. There have been hints about going back to fight the demons in their own dimension this time or maybe down to Azshara.
I've been playing a bit with Pet Battles which have been surprisingly addictive and jumping in and out of the new raids. With the Looking for Raid concept and raids broken into small wings, it only takes about an hour or so to knock out some easy raid content. Some nice solo stuff that's been put in so there is always something interesting to do. The latest patch added an island where you can gear every 90 you have to raid quality gear, so gearing isn't a concern at this point either.