This is why it would be better to do solo movies first, the least successful character's don't appear or get recast and the most popular lead the film. It has better chances of some character carrying the film due to their popularity in their Solo films. I think Cavill is contracted for 3 movies. I say WB should just gun it and go ahead with casting him as supes in Justice League or else we are back to square one with a new superman and testing the audience on him all over again.
I hear Cavill signed on for three Superman movies. If the first one does do well then and they don't cast him in JLA movie we will have two different actors playing the same charcacter and that seems rather pointless.