I think they should leave it as a one-off. It nicely bridges the gap between the movies and helps build up Penguin as a primary villain so they can hit the ground running in the next movie. Adding a new season just makes it weird if Batman isn’t in there, because then where the hell is he while all that is happening? Unless Penguin is relegated into a minor character in the sequel films, it doesn’t make sense to do a show in parallel.