We got slightly different concept.
We got a complete system(core) repo, and arch’s core repo is disabled.
What we need to do in my view, we need a modular repo based base group, which is what you also propose. A way to have a base group for openrc, or s6 or runit.
What we share is a base-devel group from system repo, since this is init independent.
I would propose I move openrc builds in a separate openrc git branch, and we could also add an runit or s6 branch. We can isolate init specific builds in branches temporarily, so the artix branch comes up as a shared init independent (“nosystemd”) branch.
Regarding @nadir post, openrc can work with s6 or runit as init as well as supervisor for openrc. Atm, openrc uses its entirely own init and supervision.