Hopefully it dies after 2 weeks as expected even if it gets released, so blizzard can finally put more resources on developing some new retail content.
The fact is, classic/bc/wotlk (Specially wotlk) have been always very popular versions of the game in private servers, and they get pretty much all the atenttion in the community who doesn't like retail.
However, never ever I've seen a Cata server that has lasted with a healthy pop more than a few weeks, it's been all over a dead expansion, and it gathers 0 interest from the most part.
MoP? It could be interesting for PVP players as 5.4 was one of the most popular pvp patches that ever existed, but aside that I see no other reason to play it because it is literally the same game as retail, just with a different spell toolkit.