I can't stand the US legacy carriers...so I would also be concerned about it, but I really think you wouldn't notice. If you gave every DM who re-qualified one SWU, you're looking at 10-20k maximum SWU's per year for CX. On a sector basis, CX has nearly 2k flights to/from JFK alone annually, over 2.5k flights to/from LHR, add in LAX, SFO, YYZ, YVR, CDG, AMS, JNB, SYD, Auckland, DXB, you get the idea. There are tons of long-haul destinations where DMs could use a Y-J or J-F upgrade.

I'm also not proposing guaranteeing the upgrade a few days in advance like UA...CX could make it as advantageous to them as possible, like only cashing it on checkin. As tedhl mentioned in his post, I think it would be a good incentive to keep people flying CX after they hit the 120k mark. I will hit probably 120k miles, doing it primarily recently on J and F long-haul, in 2-3 months after my qualifying year starts. I know I would have a greater incentive to stay on CX if I could obtain something useful after hitting say 140k or 150k miles, or re-qualifying 6 months early, or something like that. A SWU is a great way to do that, especially now that J cabins are really empty.

It is harder to obtain CX DM than the US counterparts (which would be the natural argument against SWUs, considering how bad and full the premium cabins always are on the US legacies), and there are already far fewer miles to obtain in AM.