I'd say a comic/graphic novel has become an interesting medium for world building. A much more daunting task because you are really restrained by art and storytelling. My friend during most of his college career worked on a graphic novel of sorts. It never really went anywhere with his access to the supplies to produce a graphic novel were really limited, but it was an interesting goal. I myself have always seen myself writing a novel. A world I've been working on and off on for two years is definitely a novel in my head. The other which has had significantly less of my focus is really unknown in design. I will probably be sharing the second one soon because I think its a pretty interesting concept on what is out there right now, it's just early in its development.