The ending will certainly dictate how things go forward. I doubt Nolan leaves too much opportunity for spin-offs from his universe.
But, Catwoman hasn't even ever been big enough to be the major villain in a Batman movie. She's always the secondary "villain" or anti-hero ... alongside bigger villains of Penguin, and now Bane. She hasn't been judged big-time enough to carry half of a Batman movie, much less her own franchise.
And, her interplay with Batman is one of the defining characteristics of the character. You lose the Batman influence pulling her back toward the heroic ... you're left with a small-time petty thief in a catsuit, and a pretty mundane movie. The character is largely defined by her relationship to Batman and Bruce Wayne.
I just don't think a Catwoman movie (or cartoon series, or TV show) would work without Batman.
KBZ