You know that's a good question. I'm guessing you can still use Babylon if other players don't have it. I mean, in theory your idea should work for Civilizations being DLC, but anything that changes gameplay I think would have to be an expansion. Judging from the way they had a bonus Civilization like that as a bonus, I tend to fear this might be the path they're taking.
I don't really mean to say your idea is bad. I just don't like all the DLC that companies are doing nowadays. I would rather pay more for the game with everything in it than to pay one price for the game and then pay so much extra for DLC, that usually comes after I've beaten the game already.
My thought is, when I was a little kid, back in the early 80s, you could pay anywhere from $40 to $80 for a new game. When the Playstation came out, Sony capped the game prices on the system at $40 or $50, I can't remember exactly. Everyone else just kind of had to follow suit. But my point there is, that since the early 80s inflation has pretty much tripled or quadrupled the price of everything from a gallon of milk to a new car. There's not much that's the same price as it was 20 years ago. Video games, if anything are cheaper, and you know it costs a lot more to produce a game today than it did then. If you think about it, based on inflation, a new video game should run between $100 and $150 easy, if not more. But since no one would pay that, they release a core game and then make that next $50 up in DLC. If you think about it, it's really our own actions that have spurred the DLC craze. I'm like a lot of people, I want the whole game when I buy it. But then I would also be willing to pay more for that up front.
The price of video games is just about the only thing that I can think of that inflation hasn't affected. Even a movie ticket costs about 3 or 4 times as much as it did in the early 80s, yet games, if anything, are the same price or cheaper.