This type of succession would allow the studio to stick to its established continuity. Affleck's Bruce would become the DCEU's version of Nick Fury, more or less, running an officially sanctioned League while recruiting and training for the next potential invasion. This would allow him to investigate, in true detective fashion, the arrival of Darkseid and the Anti-Life Equation, exploring the mystery of the cosmic DCEU by scouring the globe for clues. Who knows -- maybe he'd even be the first Leaguer to make first contact with a Green Lantern.
Such a move could allow Reeves' Batverse to flourish without being constrained by Bruce's shadow, perhaps cherry-picking the best aspects of 2009's Batman: Battle for the Cowl storyline from writer/artist Tony Daniel for a big screen event.
This creates an entry point into the DCEU for characters like Tim Drake as the detective-type hero that Reeves wants in his movie, a vengeful Jason Todd (whose death was already teased in BvS) walking that fine line of being a vigilante or a criminal, and even Azrael, the crazed Batman who took over when Bane broke Bruce's back, to all join Dick-as-Batman in applying their own brands of justice to Gotham. While multiple Batmen would be a very ambitious approach, it would certainly breath fresh life into the character's big screen mythos, while simultaneously fast-tracking the history of the Bat-family without having to undertake the near-impossible task of detailing every single one of the Robins involved in the franchise.
The DCEU has to move away from Bruce Wayne as Batman if it's to show genuine growth. It also needs a younger Batman for potential Justice League sequels, and we've had that seasoned, battle-weary Batman already. Taking Bruce out of the spotlight to oversee things in a limited, cameo-esque role could even give Bruce the chance eventually reunite with his son Damian during one of his world-roaming covert missions.
A solution along these lines works, both for Affleck and for the studio as everyone look towards not just repairing the DCEU, but creating the basis for it to grow and thrive. It's an aspect of superhero storytelling that Marvel Studios got right, and which Warner Bros. needs to take note of if it's to ensure the evolution and survival of the DCEU.
In theaters now, Justice League stars Ben Affleck as Batman, Gal Gadot as Wonder Woman, Henry Cavill as Superman, Amy Adams as Lois Lane, Jason Momoa as Aquaman, Ezra Miller as The Flash, Ray Fisher as Cyborg, Jeremy Irons as Alfred Pennyworth, Diane Lane as Martha Kent, Ciarán Hinds as Steppenwolf, Jesse Eisenberg as Lex Luthor and J.K. Simmons as Commissioner Gordon.