Who would want Ukrainian citizenship? Nobody. Certainly not experienced aviators who already hold more valuable/useful passports, and are probably on a career track that leads to them becoming airline pilots and making very nice salaries.
Gonky and Mover, two veteran US fighter pilots on YT, had a video segment discussing foreign pilots flying for Ukraine....they both totally shit on the idea. The risks are too high and the potential compensation is too low. These guys have no desire to tangle with Su-35s and MiG-31s chucking R-37M missiles, likely from beyond the effective engagement range of the F-16 + AIM-120 combo.
