At this point, I really don't know if the 787 makes sense at all. I mean, the technology is already aging (It will be 20 years old by the time CX receives the aircraft by 2030 and beyond if they order it), plus there are the well-known 787 engine issues. Alongside that, everyone knows that Boeing is having production issues, with the production line really slowing down recently, and huge delays for almost every airline who is supposed to be taking orders. Add to that the fact that CX doesn't already have 787s, and it would make a whole lot more sense to order the A350 or 777X. Plus, I would much rather see more A350s joining the fleet than the 787 which would definitely have narrower, less comfortable seats, in an aircraft that I would argue is less comfortable overall.

The 777X could be a good option, however, nobody really knows when it will enter service, and how long it will take for Boeing to deliver the aircraft if Cathay does order more. The A350 also does have a long backlog, however, it is a known quantity for CX, they already have fleet commonality, and it has performed very well for the airline (plus, their best product is on the A350, so more of those would be very good to see!), so I think that unless Boeing offer CX an amazing deal, it will probably be the A350. I wouldn't be shocked at all to see a mixed order of the 777X and A350 either, but I really would be shocked if the 787 is ordered.