This is currently being added to President Infinity.
There are two new options, ‘Pop. Vote’ and ‘Two-Round’. Both of these are being implemented for the upcoming French Presidential election.
‘Pop. Vote’ allows for direct popular vote to determine the winner on the national level, and causes the game to ignore the ‘seats’ numbers. This is useful for not only the French Presidential election, but various plebiscites such as the Brexit vote. (This is not the same as proportional representation, but is rather a ‘winner-take-all’ or ‘first-past-the-post’ electoral system. PR on the national level probably also will be implemented in the future.)
‘Two-round’ allows for a two-round run-off system, where if no candidate gets > 50% of the vote on the first round, the top two go to a second round of voting.
I expect these features to be added to President Infinity in the next few weeks.