Couldn't aimbots be picked up as odd movement and be detectable on a server though? Kind of similar to how those "not a robot" checks can tell if a human is clicking on the box just by looking at the movements of the cursor.

In addition, things like textures and game-modifications could be picked up in part by things like checksum verification to make sure the client is unmodified (assuming the files are modified on the disk and not in memory)

I feel like most client-side changes like see-through walls or player highlighting make themselves pretty obvious when aggregated over multiple games. A good user-reporting system could probably catch most of these.

I definitely agree though, allowing multiple random companies to install ring 0 rootkits should not be the norm. Honestly, even a Windows-level anticheat would be problematic because it would only worsen the monopoly Microsoft has on competitive games as a platform. A new solution would need to be cross-platform or else it would only be marginally better than what already exists.