No way, they would be just cannon fodder. Worse than San Marino. Way to few people living there, for them to become even remotely competitive. Plus they can play against other regions and unofficial teams which is more balanced. If they could get one of those teams like Jersey bulls, Guernsey, FC Isle of Man into the football league system.. maybe.
Also I guess political reasons, maybe Catalonia would ask then to become a member too. Although UK has a specific setup since they have independet FA since the beginning of football, so you get one country, but four national football teams.