It would be a disadvantage to them as other nations have already played games and had the chance of winning them. It would also affect the strategic planning of managers at the start of the season as a new team would have to be considered due to this suggestion, whereby a "closed down country" suddenly joins the tournament because of a new user.
Don't see where this problem can come in because they can stay closed down for the rest of the season? I mean closing down or opening up a country would be subject to if there are active users at the start of the season. There will be no need to suddenly add a U21 NT in Midseason.
However this should only apply to U21, as I assume that there can still be players for the senior NT as well (not sure how affected it is, but U21 should have the biggest impact due to age). Unless of course there are totally no active players in the senior NT as well.
But that said, it *might* be pretty a complex system to implement and might take quite a bit of work, so I guess it's a bad idea to close and reopen countries based on active users after all xD
Another possible way is to not have U21 elections for teams that have no active teams? Then the manager would be a computerized player. Kinda beats the purpose of an election if there are no voters.