So this is just a speculation. So far there seems to be some kind of pattern on how they release heroes. Out of the blue heroes and long teases. Or predictable and unpredictable.
Ana-Out of the blue
Sombra-Long tease
Orisa-Out of the blue
Doomfist-Tease
Moira-Out of the blue
Briggite-Tease and somewhat predictable
Wrecking ball-Sure we knew it was Hammond and the champion but no one knew it was a Hamster
Hero 29-
So if they keep to this pattern I think there is a good chance it might be a hero that has been mentioned before or predictable. So I think Junker Queen has a good chance.