DDO succeeded (still in developement 15 years later) because they built a game around an already established set of rules. At least originally.
BG3 MUST remain true to form to 5e to be a grand success in my eyes. Not verbatim but any talk of walking away from D&D rules is a recipe for disaster.
Make the old school D&D nerds happy....you wont regret it.
Me and my guild of old school gamers, Tyrs Paladium, is really hoping this game is a big success.
Go into NWN 1 or 2 and try to build an Arcane Archer the way they're done in DDO. I'll wait. I can go back about 9 years in DDO, and at best, it's a hodge podge of rule sets, and some of them aren't even close to DnD, any edition. This game, right now, is miles closer to DnD than DDO. Even if we only look at pure casters. I mean, in DDO, so long as you have a blue bar, you can cast. Remember how stats from items aren't supposed to apply to whether you can cast a specific spell level? Oh, that's right, that's not a thing in DDO. The preferred method to build a Favored Soul is to dump Charisma, and then use gear to get your caster levels, and tomes.
So if they're aiming for old school DnD players, they'd probably be better served to steer clear of DDO.