This is a great idea, but something that I think that should also be addressed is Masteries, and how they work with Summoner Spells.
Instead of giving them slight buffs to the effects that they do, why not have the mastery point totally change how they operate?
Lets say you have Ignite. It does base true damage and reduces the effectivness of healing.
Instead of that, you can point a mastery point into Ignite called Conflagration(or something similar, you get what I mean.), that would get rid of the healing reduction, and instead does true damage = 2-3% of their Current health per tick, for 5 ticks, making it great to open with on a tank/tanky dps, but cant give you those running juke kills.