I don't see why a dialogue expansion would be a rotten thing, per se. Anyone shrieking 'this should have been in the game to start with' might just as wlel have said that bout the guns. And they'd be just as retarded.
Actually, now I think about it, surely more dialogue would make sense? Particularly given the interplay between some joinable NPCs and the various DLC.
You already have dialogue options added after visiting the Sierra Madre. You could send the mutant to Zion to pick flowers, or that godawful scientist chap to big MT. Or regale Rose with novel drinks collected on your travels... the possibilities are pretty much endless.