>>713364223
This game was known about for a year or two when old concept art of it got leaked. Pic related. The idea was that after Knight, Gotham would've been run down and in ruins with the remainder of the Bat Family trying to keep order in the city. There was concept art for an old Bruce drawn up and you can find it really easily by searching for 'arkham game cancelled' or something. It's really cool to see models were being made for it though which shows how far along it was in development.

This was cancelled because WB Games ordered Montreal to work on a Suicide Squad game to serve as the Origins-esque filler game between Knight and this, but when Montreal ran into dev trouble they changed their minds and management wanted a GAAS. Apparently this game's assets and concepts were then given to Montreal to make into Gotham Knights and Rocksteady was given the Suicide Squad project. This was when WB was really trying to push the Suicide Squad in marketing so it doesn't seem surprising they'd want their 'best Batman team' to do the next big DC game.