Maybe ProjectileImpactEvent could be exposed aswell.
My use case: spawn baby slimes when an egg hits the ground.
ProjectileImpactEvent could also be used to set blocks on fire that are hit by a flaming arrow.

EDIT: I just noticed that ThrowableImpactEvent is deprecated and that there is a subclass for ProjectileImpactEvent, which makes this easier.

I am hesitant to add new features as 1.12 is already at the end of the life cycle, anything I add now won't be supported (as I'm moving to 1.14 fully), so unfortunately this won't happen