This... I don't know what to think about this. Well, that's not true, it's that I don't see how they could make this work - but they must have some idea, or they wouldn't be trying something that, if it fails, will screw them over MOMENTOUSLY. If they don't cast Batman perfectly, they're screwed. While Snyder is great at the huge spectacular fighting, I don't see him being able to work with Batman. From what I know of his work, Goyer seems singularly weak at writing anything that deals with interpersonal relationships, which is the whole POINT of a Superman/Batman movie - otherwise you would just make two separate Superman and Batman movies. Moreover, the Superman and Batman franchises are both at points where people aren't comfortable with them - Batman will be a new Batman, with a new style, and Man of Steel wasn't really a Superman movie - it was about Clark Kent going through all the character growth he needed to BECOME Superman, plus beating the crud out of alien invaders - there's too many concerns about either franchise for it to be a good idea to let one be dragged down by another, particularly if written poorly
I mean, it's an ambitious idea, and if pulled off, this would be the best way to start up a whole DC Universe thing - it's just that I really don't see how this team could pull this off.