> 3D CAD apps are among the most complex UIs that exist.

I agree.

> If you want to make a good one and you only have a small team, the framework had better do a lot of heavy lifting!

I am skeptical that general-purpose UI frameworks can be a good long-term solution for 3D CAD. At times, a nice UX will need to think about many of the following at once:

    - the parametric 3D model
    - its mesh approximation
    - its hidden-surface projection into lines and patches
    - the pixels in the frame buffer
    - UI widgets.

The frameworks make too many assumptions about information being easily partitioned and limited in size.

Maybe the frameworks will help for prototyping, but if the project grows, I expect at some point they will end up ditching frameworks for the core 3D viewport interactions, and have mostly their own code in between OpenGL (or similar) and mouse/keyboard events.

Frameworks for buttons, lists, etc. will probably be fine, but even those tend to be much more dynamic in 3D CAD than in average apps.