Eh? Most apps are retina now so it's not a problem.
Photoshop and other professional software will likely never be ported to Metro because that environment has very strict limitations with what an app can do compared to the desktop. You'll likely see watered down versions like Photoshop Touch on iOS/Android. As for Metro-like scaling in the desktop--that's up to Microsoft to decide.
That is sort of the point I was making though - regarding retina - earlier. While an integer based scaling algorithm is certainly better than a 1.25x one, eventually the apps were updated to fix the issue on iOS, so I don't see why they wouldn't be on Windows either. Hopefully Microsoft is indeed allowing usage of winRT/metro DPI scaling API's in the desktop environment.
Those issues plague Microsoft UI elements as well, even though they do scale, everywhere I've seen so far, some things need more than 125% for touch, but main in your face things might be fine at 125%. They do have their work to do even on their own stuff still.
I think we both see it as a potential major problem, but I'm more thinking that it is a older/poorly programmed programs issue. My tablet screen is not even *that* high DPI and still some things are incredibly small (I can keep them small or I can use the XP scaling option which blurs them - 1.25x on what ends up being interpreted as just images to the OS. Like you said. Bad. Bad. Bad.)
I may just stick Photoshop or Lightroom on this tablet to see how they look!