While PvP worlds or items locked behind PvP are a definite no-no, It would be nice if hitting a player with a snowball caused them to receive the same debuff as when being hit by the snow spitter.
Basically you get hit, you receive a debuff. When you reach (i think?) 20 stacks of this debuff you get defeated but can revive with no EXP penalty. I think this could be a fun way to have PvP, so long as an “opt out” button exists.