Hello,
I just read some of the articles in winehq.org I thought of something to do with theming: instead of having theming use existing control functions, couldn't the code be made independent, meaning the "non-themed" code basically becomes just another theme among the others, calling the same (custom) control building functions which are designed for using a theme?
just an idea, I don't know much about the code ;)
HTH,
Joris