In the end you're left with Green Arrow, Flash, Cyborg and Aquaman, which is essentially as the JL appeared in Season six anyway.
Personally, I'd go down that route and have the lesser known members of the group in the show, thereby allowing the likes of Superman, Batman, Green Lantern and Wonder Woman to live out lives on the larger screen.
Except Justin Hartley is the only actor of the bunch strong enough to carry a new show. Remember, Hartley was originally cast as Aquaman in the spinoff. If they were to do a JL spinoff they would need to either recast the rest of the team or bring in other heroes. Maybe use J'onn J'onzz, Supergirl, Black Canary, and Hawkman.