I personally hope they don't take that approach. TES PC's are better left to dissapear after their task is complete. The Nerevarine never tried to take the Throne of Morrowind (though he probably could, power wise, and Helseth wasn't exactly popular) and the CoC never tried to become Emperor. Both exited history when they were no longer needed.
The PC's are best served as short term decision makers, facing challenges like Alduin or Dagoth Ur then vanishing. The longer their story goes beyond the end of the game in question, the greater the risk of establishing a canon personality. If the Dragonborn became Emperor, Bethesda would have to make note of the quality of Emperor the Dragonborn was, solidifying who he/she is. This would invalidate the choices players made, if they didn't match the canon, and it's the historic ambiguity of the PC's which is the cornerstone of the "do it your way" mentality of the franchise.
Just shoot it forward until after the dragonborns death and be careful to tread around any mention of his personality? The nerevarine was mentioned in oblivion, they said he left for akavir, they didn't mention why, just that he wanted to. I think they did that so that the player didn't just think 'Why doesn't that guy solve this problem' so why can't they do something similar for the dragonborn. So it's 100 years after the dragonborns time, or we only hear of the dragonborn giving written orders to the legion, with no clear explanation other than 'it's the only valid tactical decision'
Also, bethesda already seem to have canon for some of the PC. IE: The dragonborn is shown in trailers and all other merchandising as a male nord, so that's how I see him. The nerevarine is probably a male dark elf (Isn't he mentioned as a he in the passing comment from oblivion?) So why not just have the male nord dovahkiin leading the empire now that the emperor has been assassinated by the brotherhood?
The dragonborn should now take the throne, because while TM2 was a brilliant tactician, he was a useless politician. (he'd practically won the great war, or at least forced it to a stalemate, yet he pretty much surrendered. Useless

)