Pokemon isn't really an applicable comparison; BW2 was a sequel that has everything BW had to offer, whereas Revelations is completely different than RE6. It's more of a complimentary release because RE6 will still be a current gameplay experience.
When you consider DLC, which Capcom is fond of, Revelations shouldn't be getting any kind of significant DLC support (story, extra modes, etc) while RE6 is very capable of being updated with anything.
I'm hoping that when we get Revelations, it'll unlock Jill for RE6
