I recall them coming to him for a justice league movie and him turning it down. Watching this scene I can see Keaton doing it. https://www.youtube.com/watch?v=zTnIpo35z6I
I don't know if it's because it's similar to the party in returns but I was wondering if anyone had had info.
No, Keaton was never in mind for BvS. However, Keatonesque elements are definitely present in Affleck's characterisation and performance it seems. Which is fantastic.