It will be great if Larian add more enemies. But it will give you more exp, more items, more gold... I didn't think that it will be balanced.
You should try out the Enhanced Edition of Divinity: Original Sin, the first game. It had tactician mode, and they did it well then. The enemies gave more XP, sure, but you needed it, and they balanced the later acts around you having that extra XP. Let us know what you think after you've tried it!
