RQBG is not changing a lot any more because for me it works fine and some people are using it. There's currently one patch in the works, but other than that it's stable. Initially, I blogged quite a bit and put effort into good demo applications. But no feature requests or patches were forthcoming. Which is fine by me. The project was meant to be simple and stay simple.
This project takes the same approach. It is aimed to put Rust at the core (business logic) of the application and code the UI in C++ or QML. This way you sidestep the enormous work of writing bindings for the Qt libraries.
KDAB hires some of the best Qt coders, so this effort by them might get more traction. Using macros and annotations like Oliviers project is nice. When RQBG started procedural macros were not attractive yet.
This new project is on Microsoft GitHub which means I won't be contributing. I prefer to work on projects that are self-hosted by communities like KDE, GNOME, Debian instead of being locked on a closed platform of a competitor.
