Here are my thoughts:
I was really expecting the plot to be about an Akaviri invasion now that the empire is collapsing. But I still think the dragon plotline is compelling, especially because the civil war, secession, and lack of a king is a pretty compelling human backdrop. I am expecting more than one main plot thread as a result, because the dragons basically represent a common threat just as the Oblivion gates, but the capability to tell this story and the difficulties of developing a political situation that allows Skyrim to present a unified front against them make it sound cool to me.
The plot threads that would not surprise me:
-Training as a Blade and dragon hunter under the last Blade
-Dragonborn plotline achieving dragon voices
-Reforming the blades, training them as true dragon hunters, constructing your own hold/fortress to base them
-The usual guide questlines: Mage's Guild, Fighter's Guild, Thieves Guild, Morag Tong/Dark Brotherhood/Assassins
-Investigating whether Akavir is responsible for the dragons and if the Akaviri are preparing to invade (setting up next game)
-Picking either the secession side or the imperial side, going on a quest line for that, and unifying Skyrim (which would involve dealing with Whiterun cult, Morrowind refugees, etc)
-Becoming king of Skryim (before or after...)
-Defeating Alduin
Since TES main characters need to start out from essentially nothing, the only way to keep a previous game's main character is some sort of reset like this. If they want to do it, that's a plausible way.
Either way, resolving the political situation and uniting the competing factions against the dragons seems to be the only way to humanize the plot since the dragons seem more creature-like than a sentient, coordinated enemy. There would be space for plenty of gray ethical situations you could go different directions on but, clearly, to defeat the dragons you'd probably have to unite the factions some way or another. And essentially a dragonborn leader that could potentially be the emperor would be the best figure to accomplish that as the main hero. If the king's job is open, and you are clearly the natural destined leader of Skyrim, wouldn't it make a ton of sense that you'd become king? I really, really don't see it turning out any other way, at least by the final cutscene.