So yes, Doctor Doom does appear in First Steps. In the mid-credits scene, we jump four years into the future and see Sue Storm and her son Franklin reading together in their home in the Baxter Building.

There have been strong rumours online suggesting that any post-credits scene could see former Iron Man star Robert Downey Jr appear as Doctor Doom for the first time, not an especially far-fetched idea given he's currently filming for his part in Avengers: Doomsday and the character is the Fantastic Four's most famous foe.