With on-going work to integrate xdg-open into snapd (PR) xdg-open becomes more widely available to snaps. snapd will also be fully in control of the implementation. It seems like another step to make it more easily-accessible would be to untie it from the
unity7 interface. Currently, the interface is needed, even though xdg-open itself doesn’t depend on a particular desktop session. It’s not even X11-specific by design: terminal browsers like w3m and links are supported.
So I think it would make sense to expose it unconditionally.