I'll throw my 2 cents in here. I'm thinking at least 300k-500k.
I usually don't really care about sub numbers, but here lately I've become an altoholic because I'm uninterested/frustrated in the 90/MoP thing right now. I have become seriously frustrated with the not enough resources/not enough mobs to kill/CRZ thing in the lower level zones. So many level 90's/bots farming ore and herbs it's been a struggle just to try and level professions while leveling. I have come to detest CRZ. I know not everyone dislikes CRZ but I also know many do so I'm thinking it might have an impact on numbers. I seriously hope Blizzard has plans to fix this somehow. Bump up spawn rates or something.
I'm not trying to add to or start a flame war about CRZ. I'm just stating my personal opinion on why I think subs will drop.