I would also love a continuation of class stories. But isn't it an extremely expensive endeavor? The current budget (especially with EA around) probably doesn't have room for that kind of undertaking. Voice talent--GOOD voice talent--isn't cheap. Re-hiring all the voice talent for more extensive dialogue if the game is suddenly more successful and EA/Bioware has the money to blow could mean said voice talent charging a higher rate for their services.
I think money and EA are the biggest obstacles here, in that right now I don't know that swtor is actually generating enough extra money to justify such a large project, and I think we can all agree EA would rather sprinkle all that money on their corn flakes and eat it for breakfast with their shareholders.
if you look at the quests on a planet each class has about 3, that's not much and if they said its to expensive i call them idiots.
I have played Makeb on a Assassin and Gaurdian and i have ZERO interest in touching it with my alts because i know its going to be 99.9% the same with only a minor amount of dialogue changes.
The next exp could easily add at least 3 or even 2 class missions they dont have to be huge but they would give me a incentive to play through with all my characters, if the next exp is exactly the same as Makeb then i doubt ill continue subbing this game and i doubt ill continue playing it.