Could also be an interesting way to up the level cap.
The level cap isn't there because "They simply ran out of game to let you level up in" it was there due to them deeming higher level spells not feasible to implement into a video game.
Modders already have done things to up the level cap to 20 in the current game, though I can't comment on its balance.
In regards to NG+, you can just console command to level your party to 12 and generate all the items from your builds to emulate a NG+ mode.
If you're wanting a more transformatice NG+ experience, that'll take more work (Such as if you want all enemies to be 12th level too) and will be up to modders to sort out.