> You could just have head and hand tracking with the rest of the body rigged and animated separate from the tracking. Player doesn't control the legs, they just dangle and animate.
But you cannot feel that way. Yes, you can render it. You cannot make a player actually feel like they're there. You can't have fun doing loops like that. Even if we could somehow suppress the immense nausea of doing it, you would not be having fund doing a loop because you are not doing a loop. This is the big lie of VR. It's just the eyes, not the body, and there's a huge difference. You arguably get more bodily immersion with a 3rd person view watching your avatar's body do things.
"I am the person I'm watching doing the thing" > "I'm literally me, and I'm going to try to believe that the weird body ik is what I'm doing".
Ready Player One (which I don't like but is the poster child for fake VR UX) does this a lot with subtle things, like the characters jump from a precarious ledge and then struggle for balance on the precipice. That's impossible to achieve! You may struggle for balance irl, you may put balance mechanics into your game, but you cannot force a player to FEEL off balance because their VR foot is now on a ledge.
> I would say the least realistic is the fine grained tracking and handling of things as thin as cards. Hand tracking isn't tight enough to manipulate a hand of cards naturally yet. That said, if you give some leeway to what the first person UX is vs how other avatars are displayed, its not so far off from whats possible especially if you would allow "reveal your hand and have it float away in zero G" to be pre-canned animations that the user triggers.
There's a really big gap between what they're implying and what we can actually do though. Cards are super thin, and bendy. You can stack them together. You can manipulate them with your fingers. You can fan them out and shuffle them. Paper thin collisions are not something that any game engine really tries to support. You get fake deformation (bending) of meshes, but it's always kind of shit. The physics of it is extremely difficult to do, and trying to replicate that level of precision is probably impossible in the foreseeable future for a number of reasons including the ones you mention.
Can you make a great player UX with cards? Absolutely. You can do all sorts of stuff to give the visual implication of bendy cards and shuffling and fancy finger work. But you cannot actually let the players do it with their hands. You're not there. You're interacting with a very, very high level interface to the game world. We won't ever get the user experience meta is implying. It's pretty much impossible without a fundamental shift in how game engines work.