Bhutan has a unique political system, in which elections to the National Assembly ( the lower house of the bicameral Bhutanese parliament ) happen in two rounds. In the first round, a nationwide vote is conducted in which only parties are listed. The top two parties in the first round then advance to the second round, in which they field candidates to constituencies, who are then elected through a first-past-the-post system. This means that the national assembly only has two parties - the government and the opposition, even when other parties do exist.
My question is what would happen if such a system is implemented in a federal state ( Bhutan is a unitary state ), and more specifically, what would be the impacts on the dynamics of the political parties?