I wish competitors would stop saying this. It doesn't matter how good your game is or how much content it ships with, it will NOT dent WoW's subscription base. The game is here to stay.
It may be here to stay, but over time it does lose subscribers. The question is if Blizzard can bring enough new subscribers in to make up for the ones that quit over time.
I used to play but quit long ago. After the better part of a year of playing WoW I'd had enough. Yes there was new content being added along the way, but over time it became the same old thing no matter what was added. I'm sure others came along and started playing along the way, but still others have quit too. Eventually it'll slow down enough that it won't be the game everyone else measures up against.
Could a KOTOR MMO become the new champ? Hard to tell. There are lots of competitors in that area. More competitors trying to get more customers for themselves from a somewhat limited potential pool of customers. EA hopes to see the market expand and it might, but they may very well continue to see a struggle to get people to play games on PCs while the PS3 and/or Xbox 360 (or whatever replaces it over time) continues to sell into more homes.