That's nice to have. For both GIMP and the industry's sake, priorities should be:
- good UX
- feature-wise competitiveness
- in any (sensible) format
GIMP is an alternative to Photoshop. It isn't a psd reader.
Being the format jack of all trades yet master of none isn't too great of an idea. It'll just exacerbate GIMP's main current problem: an ancient UI Photoshop enthusiasts dread. A lot might consider switching if the bad GIMP UX was better than the also-bad Photoshop UX.
If I had to say what my main design gripe with gimp is, that'd be modularity. Seperate the ui (skins) from the tools, effects and rendering (formats). The UI is especially egregious in its hard-codedness while effects are pretty well-supported.
A few more apis would go a long way. Hell, even the closed Photoshop has open(ish) apis, since even Adobe know the value of an ecosystem and not just their internal r&d department!