Why not? More computationally intensive things are done to calculate lighting in a lot of modern games as I alluded to. Yes it would increase the load on your CPU but that’s less of a problem nowadays with higher core counts and clock speeds and it’s not like modern anticheats don’t steal some CPU cycles already. I think you underestimate the power of modern computers. I’m not trying to be condescending here but it is worth remembering that gigahertz means BILLIONS of calculations per second.
We’re only talking in theoreticals right now anyways, it is entirely possible that a game studio has tried this and it hasn’t worked, I just don’t put a lot of faith in modern game companies.
It could be a client-side check with verification on the server. Basically transmitting which places are in view. Ray casting like the other person said. Not raytracing which is much more computationally intensive. A server side check basically so that the client can’t just say they’re looking around every corner at once.
If the trajectory and speed says either the client or another player will cross a wall soon where the player sees them THEN it could send the data to the client. You need some tolerance for ping up to maybe 200ms but that’s it. Wallhacks could give you at most a flash of a couple specific people.