ESO isn't positioned as a true competitor to WoW but an alternative. Wildstar on the other hand is positioned squarely as a "WoW Killer" (although not for me). So I doubt they are worried about ESO since it appeals to a totally different type of gamer.
Honestly I played both ESO and Wildstar a bit and neither appealed to me one bit (if they were f2p I'd likely check one or both out, but not as a paid sub), in fact I could barely last 20 minutes in Wildstar before I was basically like "What the hell is this?" and stopped. Just nothing that caught my eye or attention, with graphics more cartoony than WoW (although to be fair that's the intent). ESO I think it was more that I despise the controls on the PC; if I was playing on a playstation or something then I might have enjoyed it more.