^ I don't think that fans really want to start with the villain and work from there. It's just that sometimes it's easy to either fall into that trap or look like you have when you're discussing possible villains. I'm guilty of both myself.
As for treating these movies like a TV series, I'm guilty of that too, mainly due to wishful thinking. I do wish that Nolan's Batman was a TV show. Imagine everything we'd get to see if it were. Since it's not though, we're left with a set of movies that serve as an introduction as you pointed out. Is there room to include several of the big villains as well as an original bad guy in 3, 4 or maybe 5 movies? I think so. We already got the perfect set-up. We have a lot of bad people who were let out of Arkham in the first movie and this has to be dealt with further. We also have a few colorful characters who are either trying to imitate Batman or trying to become troublemakers with their own signature styles like the Joker. That's another good set-up right there and both work naturally with what we've seen so far. All they have to do is figure out how Batman will deal with all that while he's being hunted. Also, as mentioned many times in the past, the old villains we know don't necessarily have to be front and center. They can get the same treatment that The Scarecrow got and serve as sidestories or even simple nods. That would solve the "crammed in" feel. I wouldn't mind seeing a brief 5 minute scene involving some nut job with a home-made nitrogen blaster that Batman takes down pretty quickly.
So there you have it. I think it is possible to give us the old baddies along with some new ones all without ignoring the introduction story or looking like things were forced in. In fact, they've already been doing it, all they have to do in continue on.