Originally Posted by Drath Malorn
That being said, it took Larian until Patch 5 to accept making Disengage an Action and separating it from Jump, as well as removing Backstab. It took until Patch 6 for Larian to accept removing Advantage/Disadvantage for High-Ground/Low-Ground.
I'd estimate that, unless the game's code is really a hot mess, the removal of both of the Advantage bonuses could probably be done by a single developer in a half-day, and giving Disengage to our character was another half-day. With plenty of time for coffee with colleagues. Hence why I assume it was mostly a matter of Larian accepting to try it.
Adding a D&D mode sounds like a very complex request.

So I feel like jumping on the bandwagon, and joining the "Shove should cost an Action" clamour, since it seems to be the one riding high at the moment. Then maybe "Hide should cost an Action", "add the Dodge action", "add the Ready action", and "add proper Reactions". By Patch 11, the rules set could have become closer to how I think it would work better.
On the bright side, these changes have slowly moved closer toward 5e rules, and Larian is allegedly working on a reaction system. The list you gave plus spells (learning from scrolls and quicken), monsters jumping, and removing automatic sources of damage would go a long way toward matching 5e. If all of those are implemented, then there might not be a need for a 5e mode. The biggest remaining things would be NPC stats and short/long rest modifications, which is admittedly are much bigger asks than simply changing combat mechanics. (And I've already said I don't think the former is necessary for a '5e RAW' mode). The rest would be small, more acceptable differences: e.g., haste potion length, weapon ranges, spell durations.