Speaking of the JLA, I highly doubt that next year's Man of Steel is going to have any connection to a JLA film if and when it materializes, primarily because Christopher Nolan has said that he has absolutely no interest in being even remotely involved in or with the establishment of a shared universe akin to what Marvel's doing with the MCU,
I'd take it as a given that Man of Steel won't set up any Justice League stuff in the manner of the way the individual Marvel films have been setting up the Avengers for years.
But just because he won't be involved in the Justice League movies it doesn't necessarily mean the new Superman won't be involved... or that, say, Zack Synder wouldn't be involved in some fashion.
The Joker was only 'off-limits' because Christopher Nolan did not feel it was appropriate to re-utilize the character following Heath's death; if someone did step into Nolan's shoes and do a continuation of the universe he established with the Dark Knight Trilogy, they would in no wise be beholden to the personal choice that Nolan made.
But at this point you're asking the question: Why continue the Nolanverse?
You have a new director, a new Joker, and very probably a new Batman (unless you convince Christian Bale to take up the cowl again). The connection to the Nolanverse would mostly be that the film undermines the intent of how Nolan concluded his last movie.
When you reach that
point as a fan we're better off with a clean reboot. New Joker, new Batman, new director, new direction