Developer Ikey Doherty wrote a blog post today on the development work going into Budgie 11, the next major version of their desktop. They are working to "deGNOME" their desktop due to consistently hitting API/ABI breakage and other changes with each GNOME release.
Due to the headaches in maintaining Budgie against the moving GNOME/GTK target, and other concerns, they are shifting their development focus. Aside from working to be less dependent on GNOME, they'll also be working to eliminate their usage of Vala.
While the GTK tool-kit itself gets done much of what they need, they have decided to migrate to Qt given its C++ focus and fitting most of their desktop needs.
They will begin using Qt5, but will not be making use of QML nor will they be using KDE Frameworks / KDE libraries nor will they work on Plasma compatibility. With Qt they will still be looking to using GNOME applications.
More details by reading this blog post in full.