As the title implies, it would not only be your keystone, but also occupy one of your Summoner Spell slots. I imagine it would have to be pretty impactful and possibly have some kind of passive effect. One idea might be to bring back some iteration of Clarevoyance or Revive, if not bring in an entirely new one. What do you guys think?
Dead flag blues2 votesHexflash
Kairoptra1 votesThat’s a rune that interacts with a Summoner Spell that already exists and can be taken regardless of if you take the rune. That does not fit the description of what I’m talking about.
Frontline Fury1 votesMakes me think of the grenade launcher attachment occupying a perk slot in older call of duty games.
Eedat1 votesIsnt Predator kind of like Ghost on your boots slot?
Kairoptra1 votesKind of, but I’m talking about something that goes into your Summoner Spell slot.
Lord of Math1 votesResolve keystone 
E.
Draehl1 votesI'd love an Exhaust+ keystone for supports who really, really want to be anti-burst. Longer range, brings back the attack speed slow it once had, and hits other champions within a small radius of your target. I really don't like Guardian since you have much less control on when you activate it.
While a completely new summoner spell would be amazing, maybe altering Unsealed Spellbook to tweak the effects of existing summoner's would be more realistic.
Kairoptra1 votesActually, there is an Unsealed Spellbook update on PBE right now: https://2.bp.blogspot.com/-BMdnUE5UBdk/WsagpvNvTYI/AAAAAAAA820/7EYA39gJ30EqWidqKsdy-K7QZy5hdTclwCLcBGAs/s1600/spell.jpg
