Bg1 using 5e rules with solid graphics but keeping the story mostly intact, only minor changes to stuff like quests? Real potential. Wouldnt be that difficult to balance. It could probably be done now by an ambitious bg3 modder and work out even.
Bg2 gets really weird with the power creep of levels and its massive power spikes, so balance would probably become a challenge. The initial systemof grinding to then move to getting imoen as a forced sidequest mechanic early may need to be looked at, and the holdings or whatever like the keep for warriors, real room to expand on that well beyond what bg2 did. The cleric one even had a thing where you should tell a dude to be a cuck and it works out and if you dont his life sucks so the devs will CERTAINLY wanna bring that back!
The key is just not fucking with the main story. At all.