The github issues are nothing more than a wishlist. There doesn't seem to be any serious plans for this feature and no one seems interested in working on it. Limiting the user would require rewriting a large portion of the Qubes tools since they assume that the user has unrestricted access to the Xen API. I have looked at the feasibility of doing this myself in hopes of using Qubes in a corporate context but after looking into the architecture it became clear that I would never have time for such an undertaking.

>in the future a "qube" will be able to run on independent hardware

Qubes Air is vaporware and not under active development. There isn't much more to it beyond that blog post.