So, just as the original article I heard this from made clear, I also want to make clear, this is all RUMOR and SPECULATION, so take it all with a grain of salt.
According to a friend of someone over at the website Batman-On-Film, word on the grapevine is that the new Matt Reeves standalone ‘Batman’ movie is NOT going to be a part of the main DCEU canon. Yep, it is going to stand apart from ‘Man of Steel,’ ‘Batman V Superman,’ and ‘Justice League,’ and be a part of its own world, giving 
Reeves the freedom to do any kind of Batman movie he wants, with any actor he wants playing Batman/ Bruce Wayne or any of his iconic villains. This would certainly fall in line with recent rumors about Affleck wanting out of the role, and would also fit with the disappointing returns from ‘Justice League’ and thoughts that Warner Bros/ DC might start branching out from the DCEU proper to try to salvage its superhero credibility anywhere it can, especially in regards to Batman, a franchise that a few years ago was the gold standard for superhero movie excellence back when Christopher Nolan was helming the franchise.
As for Ben Affleck himself and his time as Batman, Batman-on-Film’s friend goes on to claim that Affleck will be given one last “hurrah” as the character in either ‘Suicide Squad 2‘ or ‘Flashpoint,’ which will be his last time playing the character and give him a chance to give the version of Batman he played a proper send-off, and perhaps death, thus making it easier for audiences to understand the Batman in Matt Reeves’ new film is NOT the same one that has been running around in the DCEU.
Of course, again this is all rumor and could be completely wrong but either way , t is a sad state of affairs for poor Batman, not to mention the DCEU, that they cannot even hold a continuity together because their tentpole movies are doing so poorly at the box-office. One would hope instead of giving up and splitting off various characters into their own universes they would just reboot the whole thing and start fresh, but maybe they have another plan over at Warner Bros, though at this point I do not have much faith left in the higher ups over there. Here’s hoping some of the releases for later this year help revive the DCEU and bring back the spark of hope that ‘Wonder Woman‘ ignited last year.
