From what I've seen in the past with lots of other games, FPP and TPP are tricky to implement simultaneously because you need to sort of build the game twice. If I build a FPP game, it's not like the 3D model for my character persistently exists in the game. It's usually just the camera itself and some disembodied arms holding weapons.
To add a TPP mode, I need to build a separate 3D model, of my character, and new versions of all the animation packages, and shadows, and etc., etc., etc. Then, I need to code a totally different camera to work with the TPP aspects, like auto-zoom and panning to avoid things obstructing my view. I'll need to code controls to operate differently if I don't want movement to feel stilted. I need to ensure the AI knows where "me" is, as the focal point will be different whether I'm in FPP or TPP.
It's actually quite a big task to do both. I would imagine that going back through a huge game and adding all of the stuff for TPP retroactively would a huge task. To get it functioning well would probably be a monumental task. Then, the bug-hunting would begin...
Anything is possible, but I'm pretty sure this would be a legendary job of work.
If there is no model there is no case... specially on a game with character customization. It would be impossible. But for the sake of argument let´s pretend a model does exist as they said you can switch to TPP and see the body when driving and on cutscenes (i am assuming in-game cutscenes as there would be no way to pre render customizable characters).
If the bodies are on those pre rendered scenes then the bodies should be rigged, right? Maybe not animated (other than the specific cinematic animations so not even cycles... let alone any complex animation or interaction with objects or the environment.
Just thinking about it is tiresome. Here is hopping the FPP is actually just an aesthetic choice and they bothered to make all the animations in case the player wanted to use a mirror or something.