Sure, no problem, this is the right place. It's not the first mod brainstorming thread, but I don't think there was one that was exactly the same.
Sure, though Japan isn't the only megalopolis in the world; think Mexico City for example.
But I'm not sure what you mean; a custom Geoscape texture with assigned maps?
What can I say? Good luck. I plan to add a Zombie mall to X-Com Files anyway.
I'm not sure how it would be a stand-alone mod, but it'd fit most mods out there.
Personally, just about every country boiled down into tactical quirks could make a valid map for any mission type, I think. Even San Fran with their rather topographically variable urban setting. (read: ramps, steep inclines, google search "lombard street")
In any case, my main point in mentioning Japan over other megalopolis areas, is that Japan has a particular level of development where the dense areas aren't either slums, or pure industrial areas, but have a similar level of density to the worst of either.
It'd be cool to see a best/worst of their originating area mod from people from just about everywhere. I figure as well as someone can sum up the differences they perceive in architecture and design compared to another country, people can kind of distill their own country into a best/worst compilation of what they feel represents their area of birth/residence.
As far as the last bits, I more meant that as a question to base the thread on: "What are everyone's ideas, big or small? TC or small mod?"
(I figure I'm confusing, but my brain is pretty confusing... so there's not a lot to do about it...)
I have to ask out of curiosity, what are your intended tactical goals/properties/quirks in the mall site/map? Are you going for an unforgiving terror site, or more a slug-fest or body-count like most alien bases? Something where you protect people like normal, have to worry about them becoming zombies/posessed, or something altogether different like how they're more a liability than a potential threat in alien bases? Either way it's cool to hear I have an idea in common with somebody. Then again the old mall level is a bit of a classic in some genres. I think it'd be good to look at the Blues Bros. a bit for mall reference, but I'm cheesy like that and love a vague reference. (on that note, Blood's mall of the dead level is another good example of this type of level.)