Okay, so it turned out that I was still subscribed under an old email address, but my mailers sends everyone with the current one. Anyway, my fault, and I would like to thank Manish for helping me out of my bewilderment. What I wanted to propose & work on after my 1.5 release is the following:
Cooperating on get an OpenDocument specification for layered raster images done and into the OASIS OpenDocument standard. Krita would use that format for its native format, of course, as all of KOffice is moving to OpenDocument.
OpenDocument automatically means some choices are made for us: a zip file store, a certain layout inside that store, and xml main document and resources for the binary data. Those choices may not be the best possible technical choices, but Krita already uses a similar mechanism and it seems to work.
And since the Gimp and Krita have a different set of capabilities, we'd have to make a flexible and complete specification, one that includes all possible (possibly uninvented as yet) color models, adjustment layers, paths (which Krita doesn't have) and so on.
I would really like to cooperate on this, since a standard used by one application isn't a standard at all and since it would mean much better interchange of documents than would be possible through either Photoshop (ancient version 6 or reverse-engineered later versions) or XCF.
I'm prepared to do most of the writing & nagging of David Faure about procedures and guidelines, but I'm not knowledgeable enough to do it all on my own.