Title is clickbait... the Z80 does not have "protected mode" (x86-specific term), in the video protection of the I/O space is implemented using additional hardware.
People talk about the Z80 supporting bank switched RAM, which also requires a small amount of external logic gates but depends on CPU features that didn't exist in every 8 bit CPU of the time. This feels similar.
Yeah, he built an MMU, which is possible for any 8-bit CPU with similar features - nice work but I don't see any previously unknown features.