I disagree about this being the last season. Time has slowed down considerably by the writers in recent years and the current season is 1924. I don't see how they advance the story up to 1939 this season.
The major pending story hook is the potential re-marriage of Mary to one of the two suitors. We might see a resolution of this matter this season to conclude the season. I have no idea and this is merely a guess on my part, no spoilers intended.
Very possible. It seems to me that they’re winding down, but it’s true, there’s time.
Before the series can end, Daisy has to become a successful and wealthy landowner, rivaling the Crawly fortune. That has been on my radar since William died and his father made Daisy the offer of inheriting the family farm. The lowliest person on the Downton ladder, the scullery maid, will rise to become the equal of the Lord of the house.
Since prequels are all the rage, the writers could have 5 seasons of the Dowager Countess starting as a debutant.