There are a lot of different franchises that could be used for a cinematic universe. I feel that a particularly good idea for this would be the Alan Moore classic "Watchmen".
Obviously they wouldn't be able to do much, but there are some great stories they can go into. Of course a Watchmen movie has been made, but though I rather enjoyed it, there was a lot of untapped potential that they could have gone into.
1. Minutemen or: (The Old Watchmen)
This movie would focus entirely on the origins of the Minutemen, another super hero group that predate the Watchmen. I feel that this story line would be great to kick off the Watchmen Cinematic Universe. Most people are familiar with the classic characters in the Watchmen, but its unclear to a lot of people as to what kind of things the Minutemen did. Lots of villains have been mentioned in Watchmen in reference to the Minutemen so they would have no shortage of bad guys.
2. Failing Enterprise or:(Minutemen Fall)
This movie would work as a sequel mainly for the purposes of talking about how the Minutemen fell apart and all quit. This film would be difficult solely because it will be focusing more more on politics, and drama of the situation, rather than action. By the end of the movie most of the Minutemen will be gone to make way for the next film.
3. Before Watchmen (solo films)
These would be a number of movies for the origins of a lot of the Watchmen before they join the Watchmen.They wouldn't go into the origins of all of them, but there would definitely be a solo film for the Comedian. Not only is he a very interesting character, but I feel like there's a lot of places they could take him, an easy choice being Vietnam. I would also love to see an origin film for Ozymandias. He talks about his past in depth in the comics so they don't have to make up too much, and that's something I would like to see. These films are really intended to introduce some of the more complicated characters before we bring them together, like the Avengers. Because I hate to stretch things out longer then they need to these films again, will not cover everybody. If need be they could also pull stories from the actual Before Watchmen comics.
4. Watchmen Rising
This would be a flat out get together for the Watchmen. Really I care little for what they do in terms of a crisis to avert. I jut want them to get started, really I care more about the films that follow this.
5. Watchmen Falling
This film will be about the fall of the Watchmen, much like the Minutemen Fall film I mentioned earlier. It will illustrate the final amendment that gets rid of heroes for good. They went into this a lot in the comic with some heated rioting that always ended in violence that I think would be interesting to watch. Not the violence, they decline of the Watchmen in the yes of the public.
6. Watchmen (part 1 and part 2)
This film will close the cinematic universe with the classic Watchmen story. I feel it would work better in two parts giving them a chance to hit a lot more key point then they did in the 2009 film that was made. I feel that after getting to know all of the characters in previous films it will be a lot more entertaining to see how much they change over time. I feel like that will be a big factor, for instance when Comedian is thrown out of a window people will be more shocked with that intro if they know him better.
This outline for a Watchmen Cinematic Universe is one I believe will work best for doing Watchmen justice while still making quite a few films.