Because of the immense headache and volatility of doing a TV show, and an MMO, obviously these tie ins would have to be loose and flexible.
Because of the nature of TV-watching by the mainstream audience, you can't take storylines from TV and put them on the game, otherwise, the TV group misses out. If the Season cliffhanger creates a secondary problem that is dealt with in-game, that's fine, but if the next season opens, and everyone tunes in to see what happened, only to find out that... its already happened, well, that could be a problem.
Now bringing stuff from the MMO into the TV series is fine. No one is left out, and the giddyness of seeing characters only before seen on the game, or having the latest crossover, raid or developing storyline mentioned in dialogue could be... well... it could be amazing...
It could be a WoW killer.