Couple of things:
1. WoW will not have a 'last' expansion until subs are at least below 1M. That is many years off.
2. I played from beta to the end of LK. TBC was easily the best expansion of WoW I have played. Seen Cata/MoP videos/patch notes and neither offered a sufficient hook. A big black dragon? Meh. Fighting pandas in what is effectively China? Meh.
3. A story worth paying attention too - like Burning Legion - would definitely get me interested. I'd want to know what they're doing to mechanics and the rest of it but I'd give it a serious look.
---------- Post added 2013-06-30 at 08:47 PM ----------
Blizzard hasn't exactly been churning out the awesomeness these days. Diablo3 wasn't awesome. Starcraft wasn't either. Titan better knock some socks off or Blizzard may have no choice but to milk it's cash cow.