It's gonna be a long ways off before the instance gets opened. I sure hope people do, as I'm hoping to kick Kel Thuzad's ass so hard he respawns in lumbridge
But really, think people will be dedicated enough to get that far? I hope so
MC and BWL are basically cakewalk. So there's only really AQ40 that people have to get through to get to Naxx. I think lots of people will be dedicated enough to get there, but I'm not sure about how many will clear it.
Biggest challenges are gonna be ragna(with shit stuff)/chroma /nefa/twins/ouro/c'thun (looking forward to try c'thun's script) maybe huhuran also as you have to farm your nature resist gear for melee class. (and also have some good dps). Well, that should be all the really hard boss that I can think of before naxx.