@Riot have you thought of making some channel spells drain the mana over the channel instead of on c
Basically when a champion has an ability that is channeled(typically ultimates) they have the same mana cost as live but drain the mana over the channel duration.
I'm talking champions skills such as 
R, 
R draining mana with each shot, 
R, and 
R.
I do not mean channels such as Fiddlesticks Drain or Velkoz R(maybe make Velkoz R work with the drain mana thing). If fiddle W could be draining the mana over time he would be god tier.
The big question, why? Well it would help those champs if their channels got interrupted almost immediately which would result in a huge amount of mana wasted for nothing. Karthus R is the best example.
But if we were to do this with Jhins R how it would work on him is half the mana cost on cast and the other half divided into his 4 shots.
