Hi Norman,
Closely related, some years ago, Daniel Collins implemented an Xpra client for Genode. Although it has remained at a prototype stage [2], the code is accompanied with nicely entertaining documentation [3] (practical experiences, discussing X-isms, various ideas).
Thanks for the pointer. I remember you talked about it, but I've never tried searching for sources. I may find some new ideas there.
Best Regards Ivan Loskutov