actually not much new code
since TPP mod can easily do it because CDPR leftover lots of frameworks in the game enough
characters for players are looking good not broken in the first person cut scene even looking from third person mod
the game begins using TPP before moving to FPP
the currents problem with third person mod is the camera is not dynamic to avoid clipping
and the animations are even kinda fine when just walking around but during combat, the animations really broken
I'm not saying it can't be done, obviously with some work it could...
But if we're being fair here, the animations in TPP look terrible. They are stiff and awkward. That's not a shot at the mod, obviously they did the best they could with what was available and it's impressive that it works. But it has its fair share of problems. It breaks the camera just by being installed sometimes, I've had it lock my camera when not even using it. IT causes the character model to show up in places it shouldn't Like just in the background of BD segments. And early versions of it really broke the animations, so it had a lot of work to do to even get to where it is now.
To do it officially and have it look good would be a lot of work. I'd love to see it, and I think it's possible it may come with the expansion next year (Hopefully early next year). But I would not expect it any time before then if at all because it will require significant work if it's going to be high quality.