The developers of ESO outright said that the "WOW crowd" is not their intended audience. It looks like it has a chance of being a great game. I want to see it be successful WITHOUT "killing WOW" and having the HUGE population that WOW does. Most of WOW's issues are from it being TOO big. There is plenty of room in the market for ESO to do quite well without even touching WOW. WOW grew too fast, and got so big that Blizzard had to build this MASSIVE infrastructure to sustain it, and that infrastructure is expensive. WOW has to have a lot more subscribers now to remain profitable than smaller MMO's.
Also, another BIG thing to point out: Zenimax and Bethesda are PRIVATELY owned companies. (Bethesda is actually a subsidiary of Zenimax.) They do not have any shareholders to answer to. ESO has a chance of being a great game, and I'm cautiously optimistic for the first time for an upcoming MMO. Let's not ruin its chances by yelling "WOW killer".