They could have something included to tie in the DC movie universe, considering all the other source material they're raking into it. I'm not talking anything huge, but something on the order of a cameo/Easter egg. I was talking about it with my brother yesterday, and it hit me that if it was permitted by TPTB, and if he were available, they might be able to get Zachary Levi to do a scene as Shazam. If they kept it brief enough, he could enter and exit the story without revealing much of anything. They could even get a gag out of it by having the established Arrow-verse characters presume he is another version of the Flash. With the red suit, gold trim, and lightning bolt insignia, it would be a reasonable conclusion. Plus, Levi strikes me as a guy who might be willing to do it, maybe more so than any of the other DC cinematic universe actors.
I presume this would not be allowed, if only because I suspect one of the goals of using Crisis is to make all these characters going forward live on the same earth, with the "alternate" versions implicitly written out of existence -- which they wouldn't want to imply for the movie characters.
SSB