In the trailer for dragonborn, Dovahkiin is riding a dragon that looks a lot like Odahviing. It's a good guess becuase it would be very awkward if you can just train every dragon you see. Anyway it seems like you ride a dragon to Solstheim (There is a boat but I mean, who's going to go to a corrupt mushroom island)

So it seems Dovahkiin rides Odahviing to Solstheim to straighten sh*t out (spellchecker is furious) but in order to do so he must first overpower Odahviing at Dragonsreach which takes place during act 3 of the MQ. I personally think that this mean that at the throat of the world Parthanax/Esbern at Skyhave temple tells you sh*t's going down in Solthstheim and you need to fix it.

If I am right then I am very glad as many people, like myself are disappointed with the main quest line. So an extension decorated with cut scenes like Dawnguard was would be awesome.

what do you think?

Not necessarily.

Nothing short of a re-write would fix the MQ.