Originally Posted by
Deathray
There are plenty of carriers that operate both the 777 family and the A350 family in volume (SQ, QR, AF, TG, CX to name a few - LH is the launch customer for the 777X and operates plenty of 350's). Fleet commonality doesn't seem to be the driving factor for a lot of airlines these days. After some of the fallout from the Boeing issues, it wouldn't surprise me if more large carriers actively look to diversify to both manufacturers. AC itself operates the 737 Max, A220 and just placed an order for the 321XLR (not to mention the legacy fleet).
All that being said, I'd be surprised by any orders for the A350 family soon. To necessitate that, AC will either need the desire to expand their high lift routes (ie 351 sized), to wait for their existing high capacity fleet to age out or to increase premium loads. From what I can recall of most of their MD&A, a lot of focus was on earnings per seat mile, efficiency and partnerships rather than growing high capacity lift. From what they have been doing, it looks like they find the 789/781 easier to operate and fill rather than trying to compete for more volume.
I consider 777 (other than 777x) to be a generation ahead of A350 so it make sense that many airlines operated both of them. Out of the airlines that operate both 787 and 350. You have the Chinese airlines that buy from both Airbus and Boeing for political reasons (Maybe Vietnam does the same?). There are also the likes of QR, ET that have a large 787-8 fleet, for which 350 is too big. On the other hand, there is the likes of JL that bought 351 as 77w replacement. I'm not sure why SQ operate both 787-10 and A350.
Another consideration is most of the airlines that own both 787 and 350 are single hub carriers with larger wide body fleet than AC, whereas AC has 3 hubs, so the operational complexity of having multiple aircraft types is more challenging for AC.