I'd love it if Superman had a fight or two with Black Adam in the comics and beat the snot out of him until he's black and blue. If nothing else, than to shut up the fan boys who think Black Adam is more powerful (when he's not) and would win (when he wouldn't).
No, I'm not interested in seeing Black Adam fight Super Necksnapper on the big screen. I think it was a major mistake for the "Shazam" movie to remove Black Adam as it's main villain, especially considering who the director is replacing BA as the main villain of the movie. Black Adam is a Captain Marvel villain, NOT a Superman villain. So, it doesn't make a whole lot of sense to place Black Adam in the next Man of Steel film as it's villain. I'd much rather see a villain that hasn't been used, such as Brainiac. Why would Black Adam want anything to do with Super Necksnapper? This should be Captain Marvel's problem, not Super Necksnapper's.
However, from a money standpoint then this move makes perfect sense. Who replaced Brendan Fraser in the Journey to the Center of the Earth Franchise? The Rock. Who breathed new life in the Fast & the Furious Franchise when his character was introduced? The Rock. Who impressed the audience with his performance as Roadblock in G.I. Joe: Retaliation, almost getting a sequel made? The Rock.
Dwayne Johnson has been called a Franchise Saver and that is exactly why Black Adam will appear in MoS 2 because the bigwigs know that franchise is in deep trouble and want to desperately save it. So, what do they do to solve that problem? They bring in the Rock so that he can breathe new life into the movie and rake in a bucket load of money for them. As if that will save the movie, though. NOTHING can save that franchise IMO, except writing Super Necksnapper as he is in the comics. But the movie creators have already expressed they are not interested in a "cardboard cutout".
I think that it would make for an interesting dynamic, as DC will probably show them to be fighting at firdst due to a real misunderstanding, and yes, they will be shown as being roughly eauals, as BL magical lightning cam hurt Supes, and His HV hurt BA. Even match up, and then will come to a truce, and go against the common foe, as think that there will eb a baddie behind their fighting!