A second chance to give us a Superman that's inspiring and not demoralizing, that's driven by kindness and innate goodness instead of fear and paranoia, whose strength isn't his godlike powers but his very human heart.
A second chance to give us a Batman that, yeah, doesn't kill, that isn't driven by angry brutality at the criminal element but rather a powerful desire to spare others the horrors and grief he endured, even among his adversaries.
Or a truly threatening but empathetic Lex Luthor...
Heck, even a Joker that's less a walking embarrassment and a truly incredible incarnation that does the clown prince of crime justice.
There's a LOT wrong with the DCEU, and a single great Wonder Woman film doesn't negate the fact that they can use Flashpoint to remedy a lot of grievances - from both fans and critics. It's a built-in excuse to course-correct and return several characters to their more idealized and beloved incarnations or portrayals.