Substitute enchanted books by enchanted gems

Instead of enchanting a book, and then using it to add to an equipment, you would enchant a gem, and then attach that gem to the item.

there would be 4 gems: ruby, saphire, emeralds, and diamonds

the diamon would be able to have any enchantment, and have a higher affinity to getting high level enchantments

The other 3 would have the enchantment list split between them. let's say for example aqua affinity goes to saphires

Since the gems could hold more than a single enchantment, this would substitute equipment enchanting. You now enchant a gem, then slap it into whatever you want.

each set of tools/armor would have limitations to how many gems you can add to them

Just for an example:

lets say Iron can have a single gem, of any type

but Gold could have 3 gems (of any type, but not 2 of the same) attached to it.

This means that you could stack enchantments in gold much more than other tool types

lets say you put an emerald of unbreaking 3, and a diamons of unbreaking 3, and then you have an unbreaking 6 gold pickaxe, which would now be usable.

Apply the same logic for gold armor. Get something with maximun protection AND maximum blast protection. Now this is better than diamond armour when facing a wither (96% damage resistence vs explosions).

If rubys and saphires were biome exclusive like emeralds, then gem hunting could be a nice mining addition. and getting a fully enchanted gold set would be very challenging, and actually worth it.