I honestly can't think of anything ``systems-related''. I guess you could do something based on MirageOS, or replicate it using a different language (if you can justify why it is better for this purpose).
GNU Hurd has a list of open issues, although I have no idea how up to date it is: https://www.gnu.org/software/hurd/open_issues.html
But it looks like you already have a very good idea of what you want, so I don't really see how could we help.