This one is probably pretty far in the future.

After completion of the entire game you unlock "newgame+".
Whenever you enter that, you get acess to new things for restarting the whole campaign/main story.
Things which might not make sense the first time around.

Goofy stuff - but for fun.
Playing as a monster race for example like a

° Harpy, more Underdark races, a Lich, a Devil or Demon

Stuff like that.

[Linked Image from i.imgur.com] <- *click*