Ideally I want the Matt Reeves Batman movie to have Ben Affleck in it. I think that would be amazing. I think talks of Matt Reeve's movie spawning a trilogy is premature, because I think its wise to first see how and what he does with the first film. We dont even know if he wants to do 3 movies, or if he has enough stories for 3 movies. 3 movies means dedicating 9-10 years of his life to one franchise and that's maybe not what Reeves wants. If that's the case I want Reeves+Affleck to do ONE amazing Batman film.
If Reeves chooses to make a prequel film with a younger actor, thats fine too. Then I want Affleck to do one more film, maybe JL2 in 2020. I would have said Flashpoint ,but his role in that is nothing more than a cameo. And yes I still maintain using Flashpoint to make any changes in actor is as stupid an idea as you get.
If JL works, and is a huge success, there might be a scenario where Ben fulfills his 3 movie contract, does JL2 as his last film. JL2 where GL joins the league, and the 7 go against Darkseid. That would be amazing, while Reeves gets to make HIS Batman film with his Batman. That would be cool, because that might be a prime Batman who is maybe 30 years old.