Alessia was a Dragonborn and founded the first empire, Tiber Septim was a dragonborn and founded the second empire, so is it possible that in future lore, The Dragomborn of the fourth era created a Third Empire and ended with the A. Dominion and started the 5th era? Cause there is a pattern here.

I believe the dragonborns are made ruler because they have the dragon blood, that can be used to light the fire that keeps the Daedra from invading like in Oblivion.

Tiber started the third empire, between him and Alessia there was also the Reman Empire. Also the end of Oblivion removed the importance of Dragonborn emperors so there is no reason to belive that LDB will become an emperor.