This would be for 1.12.2 & Up.

I noticed in the config section under 'general' that you can cap the max amount of abilities a player can have so this got me thinking... I wonder if this could be expanded to have abilities slots as unlockables up to the max cap.

There could be a config option where you can set the minimum amount of abilities the player can have. For example... if I set this value at 1 and the max cap is 10. This means that the player will start off with only 1 ability slot and will need to craft an item & use it to unlock the rest of the slots, in this case... 9 of these items will be needed in order to use 10 abilities at once since that's the current max cap.

These new items will need X amount of XP/Levels to unlock them and this value will increase the more slots you unlock.

If the minimum amount is set to -1 that means that the player will start off with infinite slots already unlocked... well... up to the maximum cap... but if the maximum cap is set to -1 then that means the slots are infinite no matter what.

To put it short...

Min: -1 | Max: 5
Player only has 5 Ability Slots, which are usable right away.

Min: 0 | Max: 8
Player has no Ability Slots and has to unlock the other 8 slots.

Min: 5 | Max: -1
Player has 5 Ability Slots and can unlock more slots as needed.

Min: -1 | Max: -1
No restrictions, meaning all slots are unlocked and can add as many abilities as you want.

Hopefully I explained this well. There could also be a configurable death penalty where the slots will re-lock if the Player gets KO'd. Just like losing an ability upon death, only... the slot has to be unlocked again.