Fun speculation about Midgardsormr:
If you read his description he clearly says something among the lines of "He assures you this form is purely temporal". Considering we got him without using an item, it's possible that he'll grow up into our mount.
Also, a bit of data-mine spoilers maybe: The actual Midgardsormr minion item that we never got to use says: "Summon Midgardsormr. Not the big one. The little one.". While this might simply mean that you'll summon the tiny one instead of the giant-Agrius eating dragon, it could also lend itself to saying we'll get a "bigger" version of him soon.
