If you want an optimistic point of view, I think what really is happening is the A350 is just a placeholder in schedules. I'm willing to bet several regular 77W destinations such as JFK/HND/LAX/YVR/several European flights will inevitably get changed to 77W's on the schedules as we get closer to the start of Summer '25. In the past I have had bookings made more than half a year out show a different aircraft type to the one I boarded on the actual day of flying. My bet is CX is still figuring out the amount of 77W pilot resources available (which I've heard is very scarce, probably even more so than A350 camp), maintenance schedules upcoming, upcoming lease expiries, frames planned to go for Aria conversion etc. Inevitably down the road we should see more 77Ws on the schedules once these factors are more apparent for Summer '25.

I get that one or two 77W frames will ultimately go into the hangars each month for conversion to Aria. But I don't think it warrants taking them off longhaul routes as extensively as the current schedules show. Otherwise where would all the excess 77W's go? Assigned to regional flying? I don't think so. If you have time for an avgeek moment and take a peak at the flying patterns of any A350 frame, you'd see their flying missions are literally assigned wall-to-wall. With no more A350 deliveries planned, I doubt that the fleet can absorb anymore ex-77W destinations to a major extent.