This is already the standard for speedruns and high-score records for certain games. Partly just because it makes the recording more interesting to watch, but increasingly it's for evidence of not-cheating.
Okay, but you couldn't just have a linux computer procedurally generating that video, then exposing itself to the host computer as a webcam over usb gadget driver?
Not to mention that you would have to comb through all this footage to detect cheaters... It is honestly a laughable solution.
Yes, but writing a program to synthetically generate correct images will take a while to come out in which players can play without cheaters ruining games.
Creating a system to automatically verify correct videos will take a while to come out, not to mention that it is extremely invasive for the end user and requires that they own all this extra equipment and bandwidth.
The cheater does not even really need to generate fake video like I've described. Aimbots can be as subtle as the cheater wants them to be, offering <5% precision adjustments which won't be visible on a webcam. Not to mention that half of cheating is just information assistance like wallhacks which this doesn't even cover.
The point is that the cheating problem is unsolvable at scale against sufficiently motivated attackers.
It would be possible to solve if the incentives are not that strong to cheat, but the status game associated with multiplayer games takes care of the "sufficiently motivated part".
It would be possible to solve at a small scale (e.g. at a tournament) by manually vetting hardware and manually reviewing footage.
But preventing cheating at scale against motivated attackers is so expensive as to be uneconomical. The devs will probably try to install whatever malware they can get away with in order to demonstrate to their shareholders that they care about it, but I'm guessing even the devs will be relieved when Microsoft just blocks their kernel-level malware because they know the risks it entails.
Can’t imagine a significant number of users ever accepting this solution, there’s too much hassle involved.
Users who are not attempting world record attempts or playing tournaments where money or fame is on the line.. in other words.. 99.99% of the user base will have no incentive to bother with webcam hand recording anti-cheat systems.
They will just move onto another less bothersome game that doesn’t require it, and that game will eat the webcam-required always recording game's market share.
There will always be servers for the players that don’t care about hackers to play on.
For the ones that are sick of having their games ruined by hackers they’ll angle their webcam down at their hands (or use the app on their smartphone) and join the server that supports it.