We already know that Larian is being forced to shut down ideas for content they want to add to BG3 in order to actually release it one day. Personally I'd be fine if they released DLC later that added in some of that content they weren't able to get in before a reasonable release date.
Ideally, for me, it'd be something like a Character Pack that adds a couple new races and a few new sub-classes from 5e sourcebooks that didn't make it into the base game. Especially if they go crazy with racially divergent stories when they add the legit monster races so that playing a goblin or lizardfolk is significantly different from playing even a Githyanki or Drow.
I definitely wouldn't say no to a full expansion that adds a whole new map and explorable area though.
