I wrote at length on this site 2-3 years ago about how Titan would be the next incarnation of a WOW MMO despite them saying it wouldn't be. Quite simply, to make a game of the scope of Wow would take years and years and there has to be a Wow 2, if not it's commercial suicide - you can't just let a game like that fade (look at everquest 1 - 2, GW 1- 2 etc). It's one of the biggest games ever seen yet it came out at a time just before mobile devices would be able to accommodate it correctly and consoles weren't brought into the plan. Now they will put the whole thing on a much much larger scale so that you can live in the game outside of being in front of your pc, console etc. Every aspect will be next generation and it will be super polished, as one would expect.
But to kill off the wow franchise by releasing these expansions with minor tweaks to the engine every few years? Nah. Not going to happen like that, Wow is much much too big a cash cow.