It's a method of communicating with peripherals. Sometimes it can be simpler, because you get to just treat things as memory.That's interesting. The new feature that won't be available for NX is "decides can access memory mapped as IO".
What's the benefit to that?
It's not especially interesting by itself, but the fact that it's a new feature that's apparently functionally disabled on "NX boards" certainly catches one's attention (unless that's not meant to include devkits somehow, but that seems unlikely from context). The notes about the page buffer size thing are similarly intriguing. It's all potentially suggestive of functionality not intended for current hardware.