I was talking to a friend about this the other day. I expressed concern for how they were going to make Frieza as powerful (if not more) than Beerus. Even at the end of Battle of Gods, it was still quite clear that Goku wasn't stronger than him.
Well, my buddy said he heard speculation (he wasn't able to cite a source, however) that Frieza steals Beerus' power or something, hence the strange liquid we briefly see him coming out of.
That's the ONLY thing I can think of that would put him on the same level of power as Goku or him being more powerful.
Frieza's return is quite obviously going to be coming from being wished back because there's no other way he could come back if they're making this canon as Trunks destroyed him completely.
Either way, I hope they do ONE thing that they did with Battle of Gods and that's make this movie have the same humor that Battle of Gods had. The humor made up for the lack of overall action throughout the movie, so it would be nice to see plenty of humor AND action all in one.
I just hope they don't screw this up. Outside of Cell, I feel that Frieza was one of the best villains in the Dragonball universe.