I would suggest that Larian develop a "D&D mode", which actually attempts to implement 5E rules as closely as possible.
I would really like that with couple worries:
1) unless Larian does some encounter design just for this mode, the game might be a complete mess/unplayable when reverted to core rules
2) would need development of new functionality (like reactions)
If they are able fully implement all of the core rules new mechanics, there shouldn’t be much rebalancing required. I agree that this might be a problem because they started to rebalance the game before attempting to fully implement 5e to the extent possible, which suggests that they have already implemented as much of core 5e rules and mechanics as they plan to implement, which is worrying.
I think they can still do a much better job of implementing 5e, even if reactions are “cost prohibitive”. There is still a lot of easy to implement things that have not been implemented.
