Previous AEX course preferred ( so retired IRE/TRE - STC/BTC). Otherwise a very long upgrade process.
My understanding is that they will not need a Class 1 medical, but will need to demonstrate and maintain proficiency through completing their own PC/RT etc.
I doubt they will be paid much extra. in addition an endless succession of PC and M3/M6 duties will undoubtably drive anyone completely insane after about six months. Oh, and guess who will be doing the red eye sim checks....
But there are over 13000 regulatory Sim sessions per year. If some Sim Instructors can cover some of those then the BTC/STC can fly more.
Safety. Phaaaa. It's all about keeping this circus on the road for a few more months.