While Ray Palmer, The Atom’s secret identity, was eventually given the live action treatment on Legends of Tomorrow, Zack Snyder has said that an alternate version of the character was originally in the 2017 Justice League movie, suggesting a solo film is possible and casting Simon Helberg would be a fun choice.
The Atom does share many similarities to Hank Pym’s shrinking alter-ego, particularly that they are both scientists who shrink.
Not to mention, Helberg is known for a spot-on impersonation of Nicolas Cage, who almost played Superman before Brandon Routh, who now plays The Atom on TV, bringing this connection full circle.