Interestingly, TVLine indicates that the Metallo that will turn up in the second half of Season 2 will be the former John Corben, played once more by Frederick Schmidt.
He was given a new mission and a new name: as Metallo, he would hunt and try to kill Supergirl and Superman.
Metallo was originally an assassin by the name of John Corben.
Evidently, Cadmus found a way to bring Metallo 1.0 back to life instead of building a brand new villain from a fresh host.