If possible, I think it is possible to transfer part of the discussion about DirectGUI to a new topic. Some forums have this feature.
While it is all the things you said, it doesn’t have markdown support which most modern gui systems use.
I made an initial effort to embed Panda3D in PySide2/Qt5 here:
If anyone has any feedback that would be appreciated.
Hm. Nothing is perfect, but I think that markdown is not that hard to implement.