That'S a nice idea, but I'm wondering if it's that usefull. I think it will please the casual player (like me) but not the usual expert you can find here whom are looking to finish the game as soon as possible. Storing scroll for future fights and having to come back to replenish your book of scrolls won't be an option for them.
I'd love the option of leaving scrolls so the mage could mix spells together and create a new one. Like a scroll of fire and a scroll of trap becoming a fire trap adding fire damage with chance of burning. Will have to see if it could be possible to upgrade those spells like the other one. Since it will become spell of another house, an hybrid one. Maybe a skill that let you learn 3rd level hybrid spell enabling you to upgrade to level 3 any hybrid spells.
I think you shouldn't be able to mix all the spell together, maybe only spell from different house. Who wouldn't want the bless/stoneskin hybrid spell for 7 mana?
