Perth Airport isn't stupid, they know someone will be flying PER-LHR non-stop by the end of the decade. They aren't going to subsidise one airline over another to do it! If Qantas shoots itself in the foot (which is most likely, given they have done it before in Perth - e.g. the withdrawal from SIN) it will probably be one of the Vigins that does it (VA or VS)! There is high possibility that BA could even come back to PER, the only reason they stated they left, was a network-wide reduction in two stage flying due to costs, so a non-stop flight alleviates this issue! Wildcard: Could even be another EU airline, depending on what happens with post-Brexit negotiations!