Discovered Synfig today which is a vector graphics animation package using gtkmm for its GUI. (Source code here). It looks very promising and hopefully they will be able to cooperate with Inkscape going forward as I assume they have some overlap. The similarities in library use should also be a plus in that regard. Would be great if Synfig got support for animated SVG files so it could be used for interchange of files between Synfig and the rest of the world, including GNOME and Inkscape.