replying to myself...
However, you know that the main application handling and, with this in inkscape at least, the main desktop widget would need a testbed before being included in the mainstream source, that's IMO the sole reason for --main-gui.
...for --new-gui should that read.
So, you might ask, what's needed before we have a Gtkmm desktop?
The todo on that is, as I see it:
-------------------------------------- Bugs - changing msg label changes window size - enlarging window doesn't recenter picture - zoom out to 1%, zoom back, no longer at the same positin
Features - really include URI input box? - bulia's selected style widget - layer dialog (because there will be no layer selector on desktop) - infamous icons/menu/actions --------------------------------------
That's all, folks! When that is done, and the logic switched, inkscape will no longer be "gtk+ with some gtkmm" but "gtkmm with some gtk+".
Addenda and help appreciated, ralf