Not a bad idea. I have used exposure 2, very good overall, nothing to stop people adding their own profiles, though the grain aspect cannot be done currently.
On the other hand, I have found, consistently better results just by using the "real thing" ;-) Of course some films are no longer available. But whilst you can emulate the look, even the grain, you don't get the other advantage, esp things like dynamic range, with b&w. But I agree with you, it would be nice to have film presets there.