I'd really not recommend messing with the default layout in Inkscape. If people want to fork GTK over the issue they are free to do so (though i'd not really recommend that either) but I think Inkscape has to assume the GTK developers will sort things out in their own time.
I disagree. Such a blame game ("it's not our fault, complain to GTK") is useless and stupid. As a user, I do not want to know anything about GTK at all! All I want is Inkscape working properly.
So if we can fix a GTK problem on our own, especially such a bad problem as this one, we must. By the way this will also be a good hint to GTK for them to fix things, stronger than regular user complaints I think.
I know that the lack of easy keyboardability has been a consistent sore point with people so I think there are plans to address that, if not already done so.
The lack of transient dialogs in Gimp (and Sodipodi) was a sore point too, and it dragged on for years with a similar blame game ("it's not our fault, complain to your window manager"). In Inkscape, this was the first thing we fixed after the fork, and everyone is happy since then. Moreover, in 2.1 Gimp finally fixed this too (better late than never...)