Variety's Justin Kroll says you can forget about "The Batman" coming out anytime before 2019. Filming will start in 2018. This alligns perfectly well with Matt Reeves taking over the project as director, but having a mega-blockbuster coming out this year, "War for the Planet of the Apes." Promotion and such for the film will probably have Reeves unavailble for most of the year.
Also, "The Batman" star Ben Affleck just announced yesterday that he completed rehab for alcohol treatment. That is another reason why a delay is a must.