I personally think it should be behind a facade. I mean, look at what's along the lagoon... San Francisco? Real city. London? Real city. Springfield? Not a real city, but an exaggerated satire of real towns/cities. Mushroom Kingdom? Completely fantasy kingdom. I know not everyone might care, but it would bother me. That's why I like the idea of a "warp pipe" taking you to the Mushroom Kingdom through a facade. That said, it doesn't exactly need to be a Tokyo facade.