Michael Keaton's Batman return in Batgirl supports the theory that The Flash will reboot the DC Extended Universe. It's been nearly 30 years since Keaton last played Batman in Tim Burton's Batman Returns, but he's set to return in a major way. His Dark Knight will appear in Ezra Miller's The Flash movie, which also features Ben Affleck's version of the Caped Crusader. Despite Affleck being the DCEU's first Batman, it appears that Keaton is the one who has a brighter future.
Details on how Keaton's Batman factors into The Flash are still largely being kept under wraps, but his return is only possible thanks to the multiverse. Footage from The Flash showed multiple versions of Ezra Miller's Barry Allen exploring Wayne Manor, and concept art teased Batman teaming up with the DCEU's main Flash. Due to the rising popularity of multiverse stories (see Spider-Man: Into the Spider-Verse and Spider-Man: No Way Home), many rightfully wondered if Keaton's return would be a one-time deal or something bigger. With Keaton's Batman now confirmed for Batgirl, it is clear that the DCEU has plans to keep using him - and it also makes the possibility of a reboot stronger.
The decision to bring Michael Keaton back for Batgirl couldn't have been done lightly. Ben Affleck is the DCEU's original and current Batman, so not using him and bring back a former actor is a big deal. Batgirl is certainly set in the main DCEU timeline based on J.K. Simmons returning as Commissioner Jim Gordon, and there are rumors of other current DCEU characters appearing, too. Using Michael Keaton's Batman upends the idea that Leslie Grace's Batgirl is the protégé of Ben Affleck's Bruce Wayne. It instead suggests that the DC shared universe as audiences currently know it could be nearing its end, with The Flash perfectly positioned to reboot the DCEU and Michael Keaton set to replace Ben Affleck as the universe's main Batman.
It is no secret that The Flash is a loose adaptation of the classic Flashpoint storyline, so changing the DCEU timeline and multiverse was always going to happen in some fashion. Keaton's Batgirl return strengthens the argument that this is what Warner Bros. and DC Films are planning. Affleck has openly expressed that he isn't interested in doing blockbusters anymore, and The Flash has long been thought of as his final Batman appearance. Instead of the DCEU continuing on without a Batman, The Flash rebooting the DCEU can solve that issue. This reset can make it so Keaton is the DCEU's future Batman, which will allow Batgirl to show a mentor/mentee relationship between Bruce Wayne and Barbara Gordon. It also prevents Batgirl from having to take place in a separate universe from the DCEU and Matt Reeves' The Batman universe.
Although there will certainly be many who will be disappointed by a DCEU reboot (especially if it means no more of Affleck's Batman), it is the right thing for the universe at this time. The vision for the shared universe has changed too much since it began, so Walter Hamada using The Flash to reset the continuity to some degree is understandable. It also allows not just Batgirl, but the whole DCEU to make a hard pivot away from Zack Snyder's DCEU, which makes sense considering the studio has made it clear it does not plan to continue that storyline.
