My suggestion: add a new loot tag that creates a random enchanted book. There should be a slider that lets you choose the level of the enchantment as well as whether or not a treasure enchantment can be received.

It would be possible right now to create an inventory generator of 50 or so random enchanted books, and use that in other inventory generators to create a random enchanted book. That's probably an effort of 30 or so minutes. It would be a decent enough approximation of the feature. I may end up adding the feature some time, but it's not planned as I'm only fixing bugs right now.