Current status of U2F proxy softtoken?

The qubes documentation page for utf proxy Redirecting… , includes the following:

…diagram depicts future work in which we plan to implement the Qubes U2F Proxy with a software token in an isolated qube rather than a physical hardware token. This is similar to the manner in which Split GPG allows us to emulate the smart card model without physical smart cards.

Anyone know the status of that?
(did not find a github issue to track it with)