Not GNOME, but the implications for GTK and a whole load of libraries that are being worked on to support these changes. Like especially GTK is just not a stable target. I used GTK 1 and 2, and especially the incompatible changes in 3 and removal of features are just super annoying (many examples, we already had the introduction of header bars etc., there was always a little triangle in the status bar that was just cut, lots of deprecated widgets, ...). And if you look at the plans for 4(!) there's more fundamental changes coming.

And personally I still don't want to touch Qt, but it might just come to that. I don't think I'm up for yet another rewrite with a toolkit that can't be stable for ten years. That might sound grumpy, but also consider GIMP is still working on the port to GTK 3 ...