I think the DC heroes that did need their solo movies before BvS, are the Superman, and Batman, yes Superman already had his solo film, but I feel the whole face off with Batman should have been his Third appearance, we should have gotten a Man of Steel 2, before BvS, Affleck's batman did need a solo film, in which we would see Robin be killed (maybe in flashbacks) it would serve to establish his more violent approach, Wondy imo is fine as she generated enough hype for her then solo movie, Aquaman should probably have gotten a solo movie before JL, I feel that Flash and Cyborg are fine with being introduced in JL and then have their individual films.
Both versions of Justice Leage end with Flash getting a job in the forensic lab essentially setting up his movie, if I was in charge I would have made the flash film the first of DC "Phase 2" films, it would have maybe Captain Cold as the bad guy, and tease Reverse Flash, but mostly as a cameo he wouldn't be the big bad yet, Here we would also have the Cyborg solo film, Wonder Woman 2, Aquaman 2, and I assume MoS 3, and Batman 2, Shazam would probably fit here as well, my overarching plot would be setting up the legion of doom as the enemies in JL 2, then "Phase 3" would start setting up Darkseid's arrival on earth. Anyways I'll take my puzzle pieces.