A Nintendo theme park with the production values of a WDW park is pretty much my ultimate dream. That'd be a hell of a fifth gate.
Franchises ripe for lands/attractions:
-Mario--perfect "main" area--plus Mario Kart would make for an awesome ride, along with the Bros. battling Bowser
-Metroid--awesomely dark sci-fi world
-Zelda--foresty fantasy world
-Pokemon--I'd love to see a Pokemon safari!
-Kirby--an ideal kid's zone
-Star Fox--intergalactic thrills with anthropomorphic animals
-F-Zero--obviously the home to the fastest, most exhilarating rides in the park
-Pikmin--get shrunk down to the size of a nickel and fight monstrous bugs with the brave Capt. Olimar and his Pikmin crew
-Kid Icarus--maybe not a whole land, but battling Medusa with Pit would make for a sweet ride
-Ice Climbers--would be an awesome theme for a massive frozen treats pavillion
It all fits together almost too well. I want this to happen. BAD. This would be one park where I would be going well out of my way to do character hunting/getting pictures... and I'm 23... anything to get next to Samus, rawr.
I think the Japanese park you guys are thinking of was a Pokemon theme park... as far as I know though it was temporary and very carnival-ish. Here we go:
http://en.wikipedia.org/wiki/Poképark