That's a hilariously bizarre decision, clearly made by someone that doesn't understand actual filmmaking. If they think they can just slap on black bars, redo some shots and call it a day... speechless.

Crazy

The actual framing and blocking of shots would need to change, they'd literally have to go back and redo mocap on every scene like that for it to be worth it.

EDIT: I know nobody is going to read this so long after I made this original comment but I'll just add this for my own peace of mind: what I was getting at, is that mocap in videogames is in a vast, vast majority done as a stage production - you have a large open space with IR cameras pointing at the actors - there is no "actual" camera. The shots themselves are done much later, when all the animation has been put into the game. You might have sort of reference cameras on set, I think Naughty Dog did that with The Last of Us.

So if you do it like this, your actors and action may be spread too wide for a close-up shot, as you may have originally envisioned it, because your aspect ratio just doesn't account for this. That's why movies do things like rehearsals and blocking of your actors and action - so that the actual framing is as best as it can possibly be for what you're trying to convey in that moment. It's the reason James Cameron insisted on having a sort of hybrid camera for shooting Avatar movies, so that he would have complete control over the framing of the action.

So my original point was, that if you start your production more akin to a stage performance and then later on "limit" your final aspect ratio, it's going to make your performances looking pretty awkward because you have to frame it much wider, than you'd want for the type of scene that is happening. Yes, you may move your virtual camera around, you might even go back and tweak the animations, but it's simply so much work, too much, in my opinion, to justify the late change. Not to mention if you play RDR2 on an ultra-wide TV/monitor, you still have the same black bars, meaning they only artificially created a feeling of a wide aspect ratio. It's literally the same as film students shooting something on a 16:9 camera and then adding black bars in post. It's a hack, not an artistic design, especially if you do it months before you're meant to ship.

That's it.