Idea is simple, to limit the number of foreign players a team can have. Like in Trophy Manager(football sim), maybe it's better to limit the number of players you can dress for the game.
I think an optimal number could be 5. That way you could still start a foreign team, but at least you would have to have backups from your own nation. And it would make the transition period easy.
- It would help the problem of tanking in micronations, they would at least need 3-4 top tier national players to compete in B3. It might weigh the scales too much though, in favor of large nation teams.
- I believe it could help keeping the active users around. It would force teams to build around national stars, which might get them more emotionally attached. I've only recently started playing the game, but trading players often, and changing your team probably makes the game experience somewhat robotic. Aside from these national players, teams would probably have one or two foreign players, who would stay in the team long term. Basically, it would force teams to make a core and build around it, which would keep them (more) attached to the game.
- On a bad side, it might make the price of micronation stars more volatile. Micronation teams might sometimes be forced to overpay, which would lead to abuse.