MarkB
Legend
Inability to use more than one swift action per round seems to have been taken into account as a balancing factor when creating some of the swift-action spells. I'd have to take a closer look at some of the swift and immediate spells (and see if I can find the recent thread compiling all of them), but I think there would definitely be balance concerns associated with allowing some of them to be cast more than once a round, even with extended casting time.