That is an interesting one to ponder.
As a punter, if I wanted to fly MEL-LHR 1-stop, and I wanted to go all the way in one go, it really wouldn't bother me where the fuelling stop was. Perth, Dubai, Singapore, Hong Kong etc - who cares? It's just an airport transit lounge.
But if I wanted to spend a couple of days enroute to break up the journey, then suddenly it does matter. If Vancouver was amongst the offerings, then that could very well be my No.1 pick. Even if it meant longer actual airborne hours.
Send me a 787 Vancouver-Brisbane and I will love you forever.
In fact, maybe I won't even fly to London annually any more. My London family can just meet me in Vancouver.
Of course, it won't have gone unnoticed by Air Canada that Qantas now fly seasonally direct Vancouver ex Sydney, and it seems to be going well enough that they may consider expanding that service as future jets arrive. So I'm sure it's not beyond their imagination that Vancouver could become a solid 787 destination for Qantas in the next few years. So there is a good chance that this is a strategic "get in the market first" play by Air Canada, to attempt to discourage Qantas launching a similar competing service down the track.