BB3 shouldn't happen for sometime and when it does it should be a solo Batman adventure, no other heroes etc.
However the next "Batman" story needs to be told in a Superman Returns sequel. Any sequel they have planned for that should be scrapped and immediately refocused into a continuation of Batman's outcast, murdering tagged status. The Dark Knight totally set up, intentionally or otherwise, for Superman to come to Gotham. Batman versus Superman, Bale and Routh, needs to be scheduled right now. By film's end Superman and Batman will be the world's finest team, but right now the table is set perfectly for them to meet. Who better to swoop in after Gotham's Golden Boy goes down than the Big Blue Boy Scout? Batman versus Superman... with Lex Luthor and Joker returning. They basically made this movie as a Timm animated feature already, but it's time to pump out this baby for live action.
Very strong argument, Torch. WB's DC films are so solid right now, that a Batman/Superman crossover seems unavoidable. The contrasts/strong personaliies of the leads as set up by Nolan and Singer match anything seen in the comics or on Timmverse cartoons, so a World's Finest
film would work. The villians and their threat must be equally grim (to satisfy the "comic realism" set) yet over the top (to wow us with the fantastic elements, of course).
I only disagree with the when
; A Superman
sequel is necessary, to further drive home Singer/Routh's version, while opening up more of Superman's cast of characters (Braniac, Darkseid, et al). A third Batman
film demands to be made (given all that happened in TDK), and by then, the lead's reputation would have (believably) spread around enough for Clark/Superman to have monitored Batman's actions, and consider him a threat of some kind.
Once we have 3 Batman and 2 Superman films, a crossover would feel "right," and (assuming it would be a hit) could set logical
groundwork for more superhero crossovers--including the Justice League (IF
the other DC single character adaptations hold up).