If the spell research / spellbook system is being overhauled, I'd like to see it done this way.
Spellbooks
Shard Spellbook -
This book is available at default.
The Shard Spellbook would encompass the current Enchantment, Restoration, Combat, Ruin (Once found) and Mastery (Once Researched) spells.
Death Spellbook -
This book is available at default to Empire.
Life Spellbook -
This book is available at default to Kingdom.
Summoning Spellbook
This book is researched.
Fire Spellbook -
This book is researched.
Water Spellbook -
This book is researched.
Air Spellbook -
This book is researched.
Earth Spellbook -
This book is researched.
Researching Spellbooks
Each of the spellbooks would function similar to the Technological research trees, except use the Arcane research.
Each of the six additional books, Summoning, Fire, Air, Water, Earth and Mastery are unlocked via researching breakthroughs in the Shard Spellbook.
Mastery Spellbook has a pre-requisite of the other five books, before it shows up as a choice when getting a Spell Research Breakthrough in the Shard Spellbook.
Researching Spells
You select a Spellbook from your currently available books and begin researching one of the book types.
When you get a breakthrough, you select the spell you wish to unlock just as with tech in Technological Research.
Spells can be Always available, Likely, and Unlikely, just as with tech research.
Magic is after all being re-discovered, just like technological research, so it makes sense to utilize the same system Tech research uses. The further you research a spellbook, the longer it should take to get the next breakthrough, just as with tech research.
Mastery and Ruin books are still researched/found, but the spells are unlocked via the Shard Spellbook research breakthroughs.
When you get a breakthrough allow a level up to be chosen when you get a breakthrough, thus unlocking the next tier spells for selection. These level ups can be likely and unlikely, the higher level you go.
Other stuff
As far as the summoning book goes, add all the lesser monsters in the game to that category, i.e. Wolves, Bears, Spiders, ect.
Keep maximum 1 summoning creature for the Fire, Water, Air and Earth books that represents the given element.
Remove summons from Life, Death and Shard books.
Add new spells to all books, Debuffs, Buffs, Direct Damage, Area of Effect, Damage Over Time, Heal Over Time spells ect.