Honestly, I think it will be a positive outcome.
@Ibeatdungeon, you have to take into consideration, that most players expect the hard grind, including the lack of new features such as, LFD, LFR, old quests you have to look up on "Thottbot", like back in the days. Blizz is (hopefully) giving the players that same feel.
The population may slowly fade. But,... you will still have loyalists that just pay. Remember, it isn't about the content.. It's about the community that develops around it. Not to mention, people that have never experienced classic will bitch about missing features that they are accustomed to today's wow. But they will be slammed down by the loyalists to keep it the way it is.
Blizz will have to launch a new client with new graphics, etc. It all depends on the outcome and I'm excited to see that very outcome play out.