Can we give Xerath's ult the nice things that Jhin has on Curtain Call?

It's hard to miss the similarities between Rite of the Arcane and Curtain Call. However, Curtain call has the nice benefit of being able to cancel the ability early to refund some of the cooldown (10% per shot not fired). Could we get this on Rite of the Arcane? It feels bad to kill an enemy on the first or second shot and just have to fire the last one(s) into a jungle camp or the minion wave, especially early game when you're not likely to have another enemy champion to fire at.

I'm also open to explanations of why this is a bad idea.