I voted for Simplified ...
Bcs traditional as described here would require complete rework of almost whole game. :-/
I think that is a valid worry in general, but in the case of combat, I think that Larian could get a lot done with a moderate amount of development work.
First, many of the deviations from 5E are separately designed, meaning they could be worked on independently and without needing to iterate. This already eliminates the main delay in Larian's development system.
Secondly, as GM4Him noted, many of these changes could be programmed as optional adjustments to the existing gameplay system, and the rest do not have to be perfect. For example, you could disable the reactions system if you don't like it, or you could choose "Easy Mode" and let every character steal all the Rogue class features if you want. This is much less work than programming Honor Mode and Tactician Mode!
Third, I think a lot of these changes are actually necessary to make the game better. Yes, there are some subjective opinions about major departures from the core ruleset, like "high ground advantage," etc., but there are also large parts of the PHB that have been refined and balanced over a period of decades, with the benefit of feedback from a huge number of players and professional game developers. There is a good reason that a lot of things in 5E are the way they are, and if those could be included in BG3, it would improve the game.
