I think reading the encryption key from memory is usually easy and cannot really be detected in any way if done from the kernel or hypervisor by parsing page tables and accessing physical memory (except by looking for known code if the anti-cheat has as much privileges as the extractor, which the hypervisor approach avoids).
In first approximation, there are only two kind of difficulty levels: the impossible things you don't know how to do, and the trivial things that you do.
I always wished that CPU/GPU manufacturers would make a "online gaming edition" with hardware level encryption/anti-cheat. I know many people would love to play exclusive lobbies where it is virtually guaranteed there are no cheaters.
