Give you a 200 damage ignite?
1.Show how many stacks you have to change summoners and the cooldown for the next stack if you don't already have the maximum amount 2.Let you swap two summoner keybindings for free (Changing Flash (D) + Ghost (F) into Ghost (D) + Flash (F)). 3.Enhance summoner spells slightly if you have the rune.
I like the idea of this, especially point 3. Unsealed Spellbook is really difficult to utilize correctly, I can only think of a few situations where someone could use it.
for Baron or Dragon maybe?
for 
or vice versa in the support role or to 
in top after some early cheese after 2 min
for Enchanters late game?Anyways I think those are fine... they're just really situational IMO. So say you had some sort of buff to the summoner spells, making them slightly unique, would help make this rune more accessible in common game areas. I'm just gonna try to list off some possibilities for each one. (I'M NOT GOOD AT THIS, FEEL FREE TO REPLY TO MY COMMENT WITH YOUR OWN IDEAS)
ONE of the following, NOT all of them
Maybe a bigger shield/shield lasts longer
Could grant a small burst of movement speed
Reflects 5% of damage taken from barrier shield to attacker
ONE of the following, NOT all of them
Grants more mana to allies
Grants mana regen buff of +10% for 5 seconds
Mana spent 2 seconds prior to cast get refunded
ONE of the following, NOT all of them
Disables incoming crowd control for 0.5 seconds
Grants movement speed based on how heavy disabled crowd control was
Lower Cooldown by 2 seconds when successfully disables crowd control (max 10)
ONE of the following, NOT all of them
Slow increased based on remaining HP
Slow becomes a decaying slow with higher initial slow
Duration increased by 0.5 sec
ONE of the following, NOT all of them
Range increased slightly
Flashing over walls lowers cooldown slightly (5 seconds? idk)
ONE of the following, NOT all of them
Accelerates to 45% movement speed sooner
Lowers slow percentages affecting user (5%?)
ONE of the following, NOT all of them
Movement speed buff increased
Heals more health but over time
Heals up to 3 allies (1/2/3 for levels 1/9/16)
ONE of the following, NOT all of them
Grievous wounds affect amplified
Duration lowered for higher damage per tick
Truesight vision now granted as AoE around ignited target
ONE of the following, NOT all of them
Deals more damage
Increased range
Increased time frame to jump to marked target
Cooldown lowered by level
ONE of the following, NOT all of them
Health gained back increased
Cooldown lowered when used on epic monsters (Dragon/Baron/Rift Herald)
Smite variations (Chilling and Challenging) deal (more) damage on cast
ONE of the following, NOT all of them
Channel duration lowered by 1 second
If interrupted, cooldown returns at 33% of original cooldown
Teleports slightly further behind normal destination on arrival (the directly behind object in direction of base arrival point)
These are just little thoughts I had on the matter, I haven't done any form of testing AT ALL so it's all just my mind being imaginative obviously some of the things I came up with would be actually broken, some others being so weak and making no difference at all.
