Server side only anti-cheat is one of the problem domains that I'd really love to work on at some point in my career. This is the type of adversarial arms race that just seems really fun to think long and hard about.
It also significantly improves people's lives. Entire online games are reduced to no man's lands due to cheaters. I remember buying a number of battlefield games a couple years ago and a number of them were unplayable due to cheaters speedhacking and aimboting. I remember thinking "this is easy to detect on the server side, why arent they doing anything".