Don't know if anyone has resigned over the change to travel allowances, but Corporate Medical have had a good look at sim instructors and discovered that they cost more medically than pilots or general office staff, so have a plan to reduce the medical benefits. This may make some SI's go to greener pastures.
For years CX and other airlines have benefitted and used the capabilities of pilots who have lost their licences due medical reasons, and yet still wanted to be involved with the airlines. However, "market forces" (don't you love that phrase now it has come back to haunt that very ex DFO?) are showing that the very moderate remuneration and conditions offered by CX for the wealth of experience and marketablility of sim instructors will not keep them in the company.
The new "Instructor for a week" deal has nothing of benefit to a line pilot. I cannot understand the motivation of a pilot who would volunteer for this. I fear that the only volunteers will be exactly the wrong people who should be training these new inductees.