What if each Mastery contained a summoner spell to choose?
I dunno, just thought about it. Everyone's just picking Teleport and Flash, and EVERYONE's picking flash unless you're Mordekaiser.
What if each mastery had a mobility summoner spell or two to choose from? Support tree could get a Lee Sin dash, (As in you get a flashed to a friend, who knows maybe give em a shield too.) The Offense tree could get a ghost that let's you actually do what it damn well says it does, ghost. You could run through 1 wall during it's duration. Defensive could get something similar to a short range dash that knocks up enemies (no damage mind you.)
Like I said, just thoughts while I'm enjoying this pizza.