Rocksteady Superman & Batman Arkham 2018: Everything We Know
6. ...But They ARE Working On A DC Game
Also listed in Kotaku's report was talk of there being major shakeups at Montreal. Project leads left, developers were shuffled around and new hires introduced. If the studio's own website is anything to go off however, it looks pretty clear that they're hiring with the DC Universe in mind.
Numerous positions are listed on the company's website at any one time, with one currently even making explicit reference to DC Comics. Seeking a 'senior systemic gameplay programmer', the listing states that applicants will work "on [Montreal's] open-world AAA title based on one of DC Universe’s most popular IPs."
Other listings also point to the title in question being an open world game, so take that as you will, depending on how you felt about Origins, City and Arkham Knight.
In any case, it's pretty obvious that this all has something to do with Batman. He fits the criteria listed in the advertisement, being one of - if not the - most popular DC character going, and with previous reports stating that they've also returned to The Dark Knight, along with the fact Rocksteady said they were done with the character, the thought of it being anyone else doesn't really make all that much sense.