Ruling needs to be changed in my opinion as I can see the "how can they are allowed to do that" argument coming up. Keep it simple, born there or your parents are that nationality then you can play if not then you play for country of your birth.
The whole Catholic and Protestant thing is becoming an escape route
IMO. It is no where near as bad as it used to be regarding this, for example quite a lot of Linfields team is now Catholic dispite all the perceptions. Same can be said for more prodominately Catholic teams with Protestants in their teams.