I can't see VA being let into the QR/BA JV. I think there's probably a good chance of QR and VA being allowed a JV but that wouldn't include BA, so QR would have to choose. Even under the QR/BA JV they aren't allowed overlapping routes so SYD is excluded (either as origin or destination).
I also think it's highly unlikely BA would switch from QF to VA, you may as well dissolve oneworld; and despite a lot of commentary, relations between QF and BA are much better than they were a decade ago. It would be somewhat ironic if QF were to switch to VS in retaliation.
As for the wet lease from QR to VA, the current approvals don't allow overlapping routes, so QR would have to give up one or two of the big four and VA take over. Would QR want to do that?