I've always thought publishers would have issues with HD emulation enhancements, but since this would only be for digital titles we'll have to buy again, it would be easy to manage.
For example, many full screen games are not meant to be viewed in widescreen. The extra screen space shows visual blemishes and geometry that were meant to be hidden.
Similarly, certain low res assets and GUIs can look atrocious, not to mention most HUDs being designed for full screen also.
So, a lot of developers might want to tweak their games before they are presented. This is by and large why I never expected this to happen for disc emulation on 360/PS3, and I also knew it would never come to Wii U for Wii games (BUT DOLPHIN HURRR-no. It isn't Nintendo's decision to present other people's games in a format other than they were originally designed for.)
Anyways, this would work fine for rereleases and will essentially make it easy for more developers to release HD updates with minimal work.