In general, I think it's a good idea. If TWC mandated the HD feed on SD channels, they would be able to use more of the screen during weather programming, instead of putting the weather maps inside the SD-safe boxes, which is a terrible waste of widescreen.
The downside, of course, is that not everyone has access to the IS2 yet, which would result in satellite feeds for many more people (which helps no one), or, if it's even technically possible, a bizarre merger of the HD feed with SD Stars.