Make an item that builds into OnHit stuff

Dagger + Combine = Runeshard Grants 15% IAS and 15 magic damage OnHit

This could be used to make the build of quite a few item builds a little less obnoxious.

Wit's End: Runeshard + Recurve + Null

Nashor's: Runeshard + Stinger + Codex

Hurricane: Runeshard + Recurve + Dagger = if this thing had its own source of OnHit damage it wouldn't be nearly so much of a trap option.

And maybe some new items, too?

Gravekeeper's Cloak: Runeshard + Warden's Mail = an item that steals enemy attack speed when you get hit, maybe?

Ionic Spark: Runeshard + Kindlegem + Stinger = combine with Hurricane for lightning strikes on 3/4 attacks!

Bloodrazor: Runeshard + Cloth Armor + Recurve = Four percent of the target's max HP in magic damage OnHit! Removing the AD from the thing would make it pretty clear that this isn't an ADC item.