Unsealed spellbook is somewhat wasted potential due to unlucky circumstances.

Imagine that instead of making your summoner spells somewhat spamable and replacable- it upgraded them(damage,healing or some other special effect). Let me explain.

Unsealed spellbook atm has 2 issues:It is in the inspiration tree as a keystone, thus you are forced to take 3 more inspiration runes. While power level of it as a keystone is good and comparable to other keystones, the overall powerlevel of the tree is nowhere near as impactful as other trees. The inspiration tree is more like jack of all trades in a sense it ia usefull for all the champions, but little to no champions excell with it or use their full potential with it. ahhhmGPahhhmmmEZahhhhm

Next most champions wont take it for its abbility to switch spells, but rather simply because they want to spam spells and/or because they have no better alternatives. For example i can see it as a viable option for some junglers like Hecarim which can then spam his ghost more often and change smite for flash to gain even futher reach into the battle field. Or some toplaners using it to gain access to both flash,tp and ignite(horrible right?) However the problem lies in the fact that these are the border cases, and these cases usualy suffer from the fact that they already have way better keystones with more early game impact.

So in order to make Spellbook anywhere near viable option for the fair amount of champions you are going to need to make it more worth or change its place with some other keystone.(ahhhmphaserushahhhm) I reccomend giving the abbility to change 2/3 shards for an upgrade on summoner spell. I took the freedom to suggest some.

Ignite- +30% longer duration. Barrier- +If unbroken excess shield is turned into healing. Flash- Takedowns and Deaths reduce current cooldown by 3 s. Heal- If used near an ally heal for 5/10/15% more. Exaust- Upgrade to previous version of exaust XD JK. Teleport- Every time an allied turet falls reduce current cooldown by 20s. Ghost- Refresh duration upon getting a kill. Cleanse- Gain complete immunity to all crowd control for 3 seconds.