Very cool suggestion!
I think a slingshot could be cool if you could fire bratbursts, healbasa, and shinobi sneeze (though it currently hides the target [self], so that should probably be modified to blind the target if fired).
I do feel that as a pure pebblet thrower, it does get outclassed by the bow, however if the pebblets fired from it had, let's say 1.5X the stun of a thrown pebblet, that would give it a home as a nice early game ranged weapon