If it is true that "som tasim - Placing you shall place" (cf. Devarim 17:15) is not a mitzvah, but a reshut (cf. Ibn Ezra there). And if what the Abarbanel (to Devarim 16:18-21:9) and the Netziv (on Devarim 17:14) say is true, namely, that there is no need for/a danger to human life because of monarchies, and that the Jewish people need not have a monarchy, but may choose a representative democracy, then in such a case would it even be necessary to elect a scion of the Davidic line at all? Would the president/prime minister even need to be male? Could the "messiah" be a woman? If the change of government does negate the promises to the Davidic line, could it obviate even a messiah figure at all?
These are serious questions. Please cite your sources.