Firstly, I just want to 'wax larianly' about how great of a game this was. Amazing game, amazing characters, amazing everything. Thank you Larian, ever so much.
So on to new game plus. No, I don't want you to rebalance the entire game around higher levels, add more magic items, or do anything that makes the game different.
What I want, and what I think would make first playthrough even better in a way,
is to offer a new game plus that allows you to start the game again, but where the engine first goes through and works out every path you have not yet selected narrativly and highlights those options in the new game plus mode. Potentially you could continue to run this process over the game at the end of every run, and eventually players, through playing would be able to see everything in the game.
I think something like this would also help first play through because if you knew this mode existed, perhaps you are less likely to care about save scumming different outcomes, less immersion breaking.
Perhaps something for the definitive edition

Anyway, love the game - continue on!