In my opinion, tdkr left it perfect for batman to return, especially in a JL film. He doesn't have to return as Bruce, only Batman, and infact super and us should be the only ones who realise bruce/bale is under that cowl.
Remember there has to be a massive threat to the world that superman cannot stop alone for them to do a justice league. And from the feal of the MoS teaser, i can defiantely see nolans Batman in this world. And Batman would only be in his lar 30's maybe for early 40's, thats not a big issue.
Personally i think you only need 5 heroes for the film.
Batman - Christian Bale or JGL
Superman - Henry Cavill
Wonder Woman -
The Flash -
Martian Manhunter -
Wonder Woman should be set in the WWII times, showing the tale of Steve Trevor crashing on the Themyscira, and her going back to that mans world. There she would fall in love with Steve and would help Steve in defeating a fair amount of Nazi's causing carnage to the world, only for her to witness Steve be killed. There she should show that unlike other heroes, she will use deadly force. There she should develop a love/hate relationship wih the mans world and return to the Themyscira, unaware that one day the World will need her once more, hence her returning for the Justice League.
Set a Martian Manhunter movie set in the 1970s or early 1980s. Make J'onn J'onzz detective John Jones and have him hunt down serial killers. Call the movie
Manhunter. The reason for setting the movie in the 70s or 80s is to set it away from modern CSI and forensics. Using DNA to solve criminal cases only came about in the late 1980s, and this movie would predate that. Maybe take inspiration from movies like
Se7en and
Kiss The Girls. Make it a phsycological thriller with a rating of PG-13. John Jones would have to rely on his telepathy to catch the killer. At the same time he learns about the human condition. Bring in his love for oreos and his fear of fire.
Throw the Flash straight into the JL movie. Have us not see how he gots his powers, and show us that he hasn't really been being a hero, like he hasn't faced off major threats like Batman and Supes. Throw in an easter egg like he once stoped a mad man obsessed with cyrogenics (captain cold) trying to freeze a work office or something and stoped a hostage situation a mecernary held (captain boomerang).
JL Plot: An unknown alien army travels to earth to invade the secret location of the Themyscira. The armys leader is interested in the olympian gods, as he claims to be a god himself. Destroying the Themyscira, Diana escapes with the aid of Kal-El. The Alien God (Darkseid) decides to set his sites on taking over the whole earth (after discovering the earth holds meany secrets and holds a higher purpose), causing the earths heroes to resurface/surface to team up to protect the earth.
