One of the mods that I have loaded for early access adds pact of the tome for warlock. I fooled around with it, and the MOD does allow selection of three cantrips from the entire list of cantrips in the game.
My point here is that it is already possible to implement this with the code that exists in the game. Larian should do it, but if they don't it can be fixed by mods if needed.
Do you have the name of the mod or a link? This is joyous news.
I think that it is Expanded Warlock. However, it looks like "Expansion" does it too (different mod, despite the similarity of name). I have them both installed, and its been several months since I've fooled around with it, so I can not say with certainty.
