Would be nice to see QF back, but as stated above, I think SQ have made the MAN to OZ route their own and I doubt there is traffic for both.
QANTAS waived goodbye to MAN and the regions traveller traffic when it stopped coming here, unless you get an offer so good you can't refuse it you'd be mad to add an additional transit on a an already long journey, especially one between T1 and T4 at LHR.