So in real life national teams, players can be brought on to the national team if they were nationalized for a set about of time.
For example for the SA rugby team to be eligible for the national team you must play on a club team within South Africa for 3 years, then you are "naturalized".
You could do a similar thing in BB. Where Utopia players need to play 3 o r4 seasons for a team in a nation to be eligible to play for the NT team... and to denote that a player is naturalized the flag is half Utopia, half whatever nation he is naturalized on. However players would only be able to play for one NT team, so if a US naturalized Utopian player played one game for the NT, he is ineligible to play for another NT. The player would be eligible for said US NT if he transferred clubs, but if within those 4 years he is never capped, his naturalization is reset.
Just a thought:).