Nintendo CEO Satoru Iwata gave some hints in an interview that appeared in today's Nihon Keizai Shimbun. The paper asked Iwata if Nintendo was planning on making Wii 3D compatible.
Responded Iwata: "If you display a 3D image, the image quality becomes extremely bad, so we'd probably do it with the next system. We're thinking that the timing should be once the 3D television adoption rates crosses the 30% mark. We're looking at the adoption trends."