personal preference really. i'd be happy if warhammer got just 1 million players. i mean i know they want as much as they can get, but i like not having all the retarded people playing with me. i mean that's the downside of any MMO for me, is some of the people. and WoW is made up of a lot of those types of people i try to avoid :\Who wants to play a graphically and gameplay superior MMO that's relatively deserted? Sure you'll have great fun by yourself or any friends you can con into it but I can think of at least 3 other genres that are free to play and can deliver equal amounts of fun.
don't get me wrong, i was a complete retard on my first MMO, but i've played a shit load of them since then, and i adapt to them like white on rice. maybe i'm elitest, but the people i play and socialize with tend to agree with me on that point. the amount of people that are level 70 in that game that really have no clue how to play their class boggles my mind. not all of them could have got their characters from ebay. well... maybe they could have.
anyway, it's beside the point i know. i agree that wow is the most successful MMO in terms of their player base and obviously their financial gain. not even warhammer will top it, that's a given. i can only personally hope warhammer gains enough players to make any given server interesting. you don't need to have 10 million players on an MMO to enjoy yourself.