Is there any appetite to take this stuff into the main rumprun-packages
repo?
To master, no, at least if it's not the official way to build packages
(which is a separate discussion). The main repo shall not become a stomping
ground for various different ways to do builds each with their tradeoffs and
status of maintenance.
Hope this is useful to someone other than me.
Probably, but to maximize the potential, a pointer to your work should be
available from somewhere else besides the mailing list archives. Suggestions
on that?