Escaping The Grave
Out of all the stories on this list, this is the most recent one released, but it’s probably the best Batman Beyond tale that we’ve seen to date. If Warner ever decides to go down the futuristic Gotham route, Escaping the Grave will be an intelligent choice for inspirational material.
The story’s simple but brilliant. The Jokerz want to resurrect the Joker. Unbeknownst to them, however, is that the clown is actually a disguised and drugged Bruce Wayne, who’s being kept alive by Terminal to obtain the Keystone. When Dana is kidnapped by the Jokerz, Terry infiltrates the gang to get closer to her. He saves her, but not before he discovers that Bruce is still alive as well. Suiting up as Batman, Terry ends up saving his mentor and stopping Terminal from gaining the Keystone.
While the arc might be too short for an entire film, it could play a critical part in Terry meeting Bruce for the first time instead of the origin story introduced in the animated series. This’ll allow us to see that Terry’s already a hero, even without the suit.