As noted on Nintendo.co.jp, the 32GB Wii U Premium Set is no longer being manufactured for the Japanese market. The site says "end of production" (生産終了) for those consoles. No word on how this impacts gamers outside Japan.
It appears that they're not discontinuing the console, but rather just losing the black version. I can understand them wanting to keep the Wii primary color scheme alive, but in my opinion the black WiiU looked much better. Anything to take that horrible fisher-price look away from the gamepad.
No idea what they're trying to do with this console over the next couple of years. Their E3 direct video can't come soon enough!