The GIMP can actually already run natively on OS X, at least in theory.
There is a build of Gtk+ which uses native Cocoa backend.
I've read several posts from people claiming they have built GIMP via
jhbuild. There is also the possibility to install the gtk+ from macports
with +no_x11+quartz+macos flags and then compile GIMP, however in my case
this resulted in a bogus pango.
Currently I'm trying to make an application bundle of Gimp using Gtk+ for
Cocoa, but I haven't had much time lately.
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