Well, be it sequel or prequel, I still want more of Team Plasma's backstory. The Shadow Triad, the blonde girl and the pink haired girl, the Harmonia history, how the flying fack Team Plasma was able to build a giant, bajillion feet tall dark, brooding castle behind the barren wasteland of the Pokémon League without getting caught, BW1 left a lot of things unanswered, or at least left questioning more about the story.
Also, is there a chance that there WILL be a 5th game??!! Now, if my memory serves me right, didn't BW1 tell you specifically that Zekrom and Reshiram used to be a single Pokémon, until the two brothers fought, and split into two dragons we now know as Zekrom and Reshiram. Zekrom went with the brother who believed in ideals, and Reshiram went with the brother who believed in truths. (Or vice versa. Don't remember which was which)
If Kyurem's true, single form doesn't get revealed, then there's probably a high chance that the 5th game will introduce it. That, or maybe Kyurem ISN'T the shell of the original Tao dragon, and that it's just a temporary power source for Reshiram and Zekrom.... Cross that out. It sounds stupid.