Well, Godzilla is an IP -- I think something involving him would both make sense. Would be an IP that would feel like it "fits" in terms of the pavilion's culture. Yes, it's an outside IP, but anything from Studio Ghibli would also need to be licensed, no? I really can't imagine them doing anything from Ghibli given its relative obscurity -- at that point, just do something historical and it would resonate just as much with the masses.
Heck, just build a freaking Mt Fuji coaster using the same plans as the Matterhorn.
I agree with everyone else about Big Hero 6. I think it's a decent fit... in Future World, being used to talk about robotics or medical technology. But not in the Japan pavilion.