As expected, Nintendo didn't openly announce the new, larger-screened DSi in response to a Nikkei article mentioning it. In a statement to Famitsu (as translated by Siliconera), Nintendo said, "Our company is not doing any interviews. We believe this article is speculation." Of course, that is merely a comment on how Nikkei arrived at that information, and not a denial of the information.
It's familiar, as well. Nintendo of America said almost exactly the same thing about Nikkei's early reveal of the DSi, so we wouldn't dismiss the possibility of a DSi upgrade yet. We're checking in with Nintendo of America to find out more.