some people don't seem to understand this bit about not being able to upgrade to captain.
its this simple...an FO can instantly be a captain if the regular captain is unable to perform his functions.
how can someone who demonstrates they can't upgrade to captain with simulator sessions and an instructor be expected to takeover if the captain eats the fish (read is incapacitated).
no airline worth its salt hires permanent FO's.
if there is a minor medical problem prohibiting obtaining a first class medical and this is the only thing that prohibits upgrade, there might be some wiggle room. but this is a rare thing.