The rumor comes from social media as pages like DBSHype shared a sneak-peek from V-Jump, one of Shueisha's monthly magazines. The reports suggest Dragon Ball Super is planning to drop an info dump on fans shortly, and it will go live in this month's magazine.
"This month's V Jump will have NEW INFO on [the] SUPER HERO Movie," DBSHype shared. "Analysis on characters, Red Ribbon Army Search files that hold the key to the story, and a comment from Toriyama!"
So it appears from the translated text that Piccolo is receiving a power-up (finally) and much, much more if you watch the trailer!
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I wonder who or what it could be?!
Edit:
Trailer is up on Youtube so you can see for yourselves