Inkscape is currently at version 0.48.2, the next version will be 0.49 and the version after next will be the first ???stable??? 1.0 with full SVG 1.1 support. While 0.49 will be a longer cycle focused on refactoring and new features, GTK3 isn’t one of the new features will see on this versions.
Unfortunately GTK3 port isn’t a goal for either 0.49 or 1.0 versions but fortunately there is already a working GTK3 port for Inkscape that we can try.