The main problem would be the character animations. I doubt they would remove books completely (that would upset a lot of players) so whatever new object was selected would have to work with the same animations. The secondary problem would be the immersion factor not so much from "it's not a book!" but rather than SMN/SCH cast their spells by tracing arcane geometries using aetherically charged ink.
A scroll could fit in both scenarios. Where a book opens/shuts would be the scroll unrolling/rolling. Easy enough to trace the geometries onto a scroll as much as a book.
An Ironworks created "computer tablet" would probably also work since aetheric manipulation is part of their designs yet I can't see how it would look significantly different from a book.
Someone had mentioned floating crystals - would those briefly form into a floating geometry then reset into a "rest" state within a box? That could work since the additional animation would be with the weapon as opposed to the character and crystal are of course aetherically charged.
Staff wouldn't work because of the character animations.
Weapon is the class/job identity in this game. They're not going to completely remake the system at this point.