It would be cool but from what I can tell the game is a departure from the old titles and being marketed to a new audience.
Honestly, if that were the case than the game wouldn't be called BG3. As that would inevitably have people wondering (and perhaps even buying/playing) BG1/2.
It's also how you market a feature. It doesn't have to be heavily marketed, and not displayed as an option very visibly in the character creation menu. And I think an 80/20 implementation would make many people happy.
Well there are trying to get old players who have played BG1 and BG2 but there also wanting new players to get into BG3
That's why limiting the exposure of the feature could be a good idea. So it's not universally marketed as a feature (advertisement), but marketed directly for BG fans (interviews, ama QA etc).
I remember Wizardry 8 did something similar, where you could import the save file of Wizardry 7, at the time a 10 year old game. It also didn't change much, but people loved it.
