I just joined the legion, seeing as i'm an imperial myself now. It's only fair,

And i completed the Stormcloaks questline on PC a few months ago and Season Unending wasn't even available.

One of the sides must still control at least two holds. So if you are in the Legion, the Stormcloaks must still have Windhelm and one more.

It's harder to get a good deal for your side if you wait that long, though.

Ahh ok, so i should not get very far then. I need to have the Season Undending quest on my playthroughs, Ulfric cussing out Elenwen is pure win.