The joint venture just did the thing it does best: ship a genuine engineering advance and wrap it in a press release that says more than the underlying event quite supports. Kioxia and SanDisk announced the “start of production” of their 10th-generation 3D flash — BiCS10 — at the K2 fab in Kitakami. The technology is real and competitive. The framing is doing some work. And the business underneath it is the most cyclical, least-cushioned corner of the memory complex, which matters a great deal for how much of this belongs in a SanDisk valuation that has already run over 750% this year.