@Apollonius - that would be even harder than GTK... All of MATE is intrinsically tied to GTK, QT would be a full rewrite, essentially a brand new desktop environment.
Also, who knows what issues does QT have! MATE is one of the most accessible DE's for blind users, for example, and QT's accessibility support is nowhere near as good as GTK's.
Issues like that are important. And as much as we like to harp on the GTK team's decisions, it's still possibly the best toolkit around.