what do you think if the Dragonborn becomes the new emperor of tamriel i mean like tiber septim he conquers all tamriel again and become emperor ? i still would have to think about it but why the hell not i mean he is Dragonborn so he has dragonblood he is a warrior or a mage (we leave that in secret lol) i don′t want him to become a god only and emperor till he got kids to replace him

Titus Mede II almost certainly had an heir.

Tiber Septim had vast legions and a megazord. The Dragonborn only has Lydia and a pet dragon.

I would believe this if Bethesda made up play as a specific race (Nord for example), with a specific name, and mostly kept us on a linear path. IMO it would be too hard for the writers at Beth to accomodate any race as being the new High King of Skyrim. This would particularly be difficult if you High Elf character becomes the high king, something that I'm pretty sure has never happened before in the history of the province. If we do get to resolve the issue of a High King during a moot in dlc, I believe it will be a already established Nord with the Dovahkiin's backing.