I don't like the idea, in case of National Teams.
National Team Staff of a country now puts effort in getting those young talents trained. If you allow such an idea in to the game, that effort can be for nothing. To mention at least one point against it.
I do however agree with MOD-Crazyeye that you could do something for the merchandising, if you wanted to. But I don't think that such an option will be an improvement for the game, if you want the merchandising money, buy and train players from your own country.