FSR don't seem to be very biodegradable, I agree this is a problem. I don't think it's as much of a problem as lead birdshot over the resevoir or live-fire machinegun excercises on lake Ontario. These things happen all the time...
Regarding the gentlemanly game of paintball, that hasn't existed since 1989. Spraying is spraying regardless of the ammo type. If anything the expense of FSR will serve to deter such tactics.
I think FSR have gone mainstream already, that cat is out of the bag.