Even better !!X-RRoD - taking cues from the early Xbox 360s.
Wow. That guy is just great. I'm a new fan.
It's quite possible and reasonable to go back on the naming. It's just that with Xbox there's never been any real consistency between devices so we've degenerated into humour, but I think going back to Xbox is a fairly good serious response to the original question.It's quite clear: the next Xbox is going to be called "Xbox". No pre- or postfixes.
Or maybe not. I personally found it interesting that at Build Microsoft didn't speak about "Xbox One", it was always "Xbox". Case in point: Building Great Universal Windows Platform (UWP) Apps for Xbox
Xbox One Service Pack One
I expect Sony will adopt naming scheme like this:
PS4
PS4K
PS5
PS5S
PS6
PS6S
...