I am currently making a save game editor for Divinity Original Sin.
Ahhh, I was working on the same thing
Good lord almighty I want this so badly. I'm not sure what your limitations are as far as what you can actually edit in the saves, but if there's a way that you could include the capability to add spells and such to the characters, that would be awesome.
Both of those are possible with the current savegame format.