I'm not sure if the people who want incomprehensibly large game worlds are crazy or if I'm just out of touch
The only super-large game I'd want to see is a super GTA. Basically, all of the US-based cities on one large map. Someone created an awesome concept of it a while back:
While it's nice, I think there's too much blank space. Seeing that, I thought of a really neat layout that would help mitigate the emptiness (especially that massive inland sea). Essentially, it'd be a 3 rows of 3 cities.
Along the top, you'd have a (new) GTA version of Seattle, a (new) GTA version of Chicago), and Liberty City. On the middle, you'd have San Fierro, Las Venturas, and a (new) GTA version of Washington, DC. On the bottom, you'd have Los Santos, a (new) GTA version of Houston, and Vice City. Each city could be driven to, flown to, or walked to (why would you, though?), but could be quick traveled to using the airports in each city. As a result, the airports would actually have interiors finally.