This is so funny because rust has one of the worst cheating situations and majority of their players are windows users, and theres lots of games that have anticheat that allows linux and have notably less significant cheating problems like marvel rivals. in reality rust doesn't take cheating very seriously because if they did they would have more server side software that detects illegitimate behaviour like tons of other games do successfully...... even most popular Minecraft servers have better functioning anti cheat that is completely server side than rust has while getting kernel access to your pc. its pathetic and lazy development tbh and this entire post from them reads like such extreme cope....
It's a very hard thing to check for though especially with how complex the world can be in games today. Even if it was feasible you don't know where a client will be in a few frames so you basically need to do a "what players can be seen from this general location" check. The higher movement speed the bigger of a volume is your possible viewpoint.
This is also ignoring all the things you need replicated even when you can't see the player such as footsteps or them shooting or interacting with something.