Suggestion

Much like ore processing, killing mobs is a tedious task that can and should be automated. But, unlike with ore processing, you don't get XP from them if they're killed mechanically by Create blocks like drills and sawmills.

Since we already have experience chunks, it would be really cool if they could be dropped by mobs in proportion to the amount you'd get -- or perhaps a fraction of that, if people feel it's too OP.

Balance concerns

So, thinking about things, balance-wise, it is already totally feasible to almost fully automate with a Create-focused modpack or even just Create and vanilla blocks.

Spawning conditions can be met via a spawner or dark room, mob transport can be handled via fans and conveyor belts, and they can all be forced into being within arm's reach of an AFK player with an autoclicker.

This is very janky, but fairly easy to setup and fairly effective. It is an entirely feasible way of gaining lots of XP while being absent. So, outside of modpacks with chunk loaders, balance isn't much affected.

I think it'd be much nicer to AFK at your farm, and then look in your collection chest and see stacks of XP waiting to be used :)