Flashpoint: Paradox
I feel, if they waned to recast, reboot, have a gap and almost a book end, then this is the way to go. Geoff Johns even said himself and i am paraphrasing 'It will be the basis and go in directions we haven't seen before' i am sure i even saw tweets from the actors who portrayed Thomas and Martha.
So have a solo flash movie, perhaps the rumoured buddy/cop movie, to really establish this universe. Have Superman feature, even Bruce Wayne just to show 'hey, look at this established universe' AM has his movie in the can so we are all good.
Then 2020/2021 have flashpoint, loosely based on the comics.
Barry and Cyborg are working on what he can/can't do with the speed force - cracks appear when he reaches a certain velocity and they look like time holes. They have some fun, dropping random objects through, then googling and seeing accounts of an umbrella falling out the sky in the middle of time square etc or a candy bar appearing in the hand of a sport star mid game, then they can see that it works but obviously they don't know how to control it. It makes Barry think about his mother, Cyborg warns him, but he goes ahead and does it. Barry wakes up with conflicting memories - he has new memories but also his old, the world is different - Batman is Thomas Wayne, superman is locked away etc. Barry realizes he has messed up Barry tracks down Thomas Wayne, explains everything to him, Thomas naturally wants a world where his son live and his wife, albeit murdered, doesn't go down the route of being a villain - a parents ultimate sacrifice. They recreate the settings for his origins and it fails, he tried one more time and it works - he has his powers.
Thomas asks to go back in time and see his son, one more time - Barry says he'll try - he creates a time hole, but it's thomas wayne, he interacts, albeit slightly, creating the butterfly effect.
Barry finally goes back to his own time line, but, not all is 100% there you ve reboots etc and recasting