It important to acknowledge that QT is primarily a C++ project even though they offers "Lite" API bindings like QML, you still have to resort to writing C++ when the project scope extends beyond what Lite API offers such as extending implementation of a given QT object. C++ is extremely difficult to bind to that it's fundamentally impractical unless someone were to go about making a full scale C++ to C transpiler which is a monumental task. Foreign Function Interface is an important considerations when talking about GUI Toolkit.
The practical options going forward are basically you either fork off GTK and maintain a separate branch or to write a whole new GUI Toolkit to provide stable API going forward.