There are keyboards with hall-effect/magnetic switches that allow precise measurement of how much any given key is held down. With that said it's be possible to map the signals from WASD to emulate a controller's left stick (at least in games that allow simultaneous kb+m and controller inputs, but that's fairly common in my experience).
I have a keyboard like that on pre-order and I'm definitely looking forward to trying it. 4mm of travel isn't much, but it should still be better than a binary signal.
I have a Steam Deck and a PS5 that I will be replacing with the Pro when it ships. So to give you an answer: I'm not going to be plugging a Steam Deck into a 4k 65" OLED TV with VRR. Don't get me wrong, I love the Steam Deck, and I also enjoy PC gaming when mouse and keyboard makes sense, but sitting on the couch in font of a giant responsive display with amazing colors is by far how I enjoy gaming the most.