Well, Fennec did run on the N9, and the primary development framework for MeeGo was Qt, but not used in Fennec (the old mobile Firefox).
Does anybody know if Sailfish or Ubuntu Phone OS use Qt because it's necessary on the hardware they're targetting? Maemo used X11, for instance, but perhaps GTK can't run on whatever they're using to display these new systems. Qt is easier to port to alternative platforms with Lighthouse.
Theoretically, GTK applications could run through the Broadway HTML5 backend, but that would be unpleasant given the apparent lack of hardware acceleration. I guess we'll just have to see what exactly these phones are using- I assume it's not X11 for Ubuntu Phone OS, since you can't just load up X11 drivers on any Android phone, right?