People said the same thing about EVE Online, and in 2011 1 million people signed up for WoW.
I'm not saying TOR can't do it I'm just saying every time a new MMO comes along everyone thinks it will kill WoW. WoW can never be KILLED, it will always have players, but can TOR outnumber WoW? Possible, no one can know.
I can see how TOR would get old, but right now they are doing a good job of keeping me interested, and they're making changes for classes that are good IMO. Honestly, it could come really close to outnumbering WoW, they're pretty high up there right now.