Thinking about it, I don't really see as much of an opportunity for a mid gen refresh this time around. "4k" hit pretty big around the middle of last time and was as good a business reason as you'd find for such a thing. Now the two "big" consoles are "4k" ready anyway, and it'll take a while for the vast majority of consumers to get a 4k hdr tv. Thus the existence of the Series S to begin with.
What I don't see is any immediate display tech on the horizon to justify another such optional upgrade. HDR will advance slowly, but that's somewhat coverable. 8k is cool looking, but I feel like the diminishing returns aren't going to make it as exciting as 4k was, movies and shows are still catching up with "4k" as it is. I can see controllers advancing, at least optionally. Microsoft would be smart to put out a feature parity controller to the PS5's, but the survey they put out shows they're possibly too stupid to do so (you don't ask the average consumer if they want to pay money for something they've never tried personally.) I can also see minor updates. Wireless charging for controllers if that ever gets long range and convenient, bigger SSDs as costs come down, newer Wifi and mediate outputs, slimmer cases and new colors, a lot of the classic stuff, but maybe not rendering upgrades.
The issue is if one them jumps into the mid gen mix, it will leave the competition in the dust. I'm not sure either is willing to risk 4+ years of an absolute power gulf considering we haven't seen too much of demanding stuff like full on RT 4k 60fps. 120hz is a thing though too, and more TVs are offering it. Imagine offering 4k 120hz across the board?
Anyway, VR could always use more power and Sony is all in with psvr2. Psvr1 and ps4 pro and connected nicknames, suggesting they worked in tandem. If sony has anything above a 1440p display, its gpu will need help, and 1440p headsets are getting old.