Having taken a really good look at Pathfinder: Wrath of the Righteous over the weekend, and just the sheer amount of depth in it – FAR more classes, subclasses, skills and abilities than anything in the 5E PHB - I don’t think Larian should have any issue translating D&D into a reasonably faithful rendition of 5E. Owlcat has a much smaller team too.
Its not a question of possibility. Its an issue of if they desire to do it. Pathfinder, and Solasta make it perfectly clear.
Exactly this. Literal 5e seems to be not the game they are making, and not the audience they are targetting.
Modding to 5e literal should be a thing though, assuming anyone who cares is capable of doing it.
Similarly, modding may enable some BG1/2 echoes, again provided anyone that cares is capable of creating the necessary mods.