One has to wonder as well, exactly how would the US even know that you obtained a foreign citizenship while abroad? Americans don't enter the US with a foreign passport. I don't believe any of that is reported on FACTA either, which treats you first and foremost as an American citizen living abroad.
The only way to weed out the info would be to require that nobody can live outside the US, which would in effect make every American a permanent resident (Green Card holder) instead of Citizen. So what is exactly the point of all this?