Hey Thomas,
I know that game engine support is not the focus of your already fantastic addon, but if you could look into it at some point it would be great.
I made this post recently about an old addon which worked on rigify (also worked on the rigified daz characters), but it’s not working in 2.8. Maybe it just requires a small fix… I don’t know… there is more detail in this topic:
Maybe you could take a look in it… or maybe do something similar to help export to game engines. Thx.