That small piece of artwork in the Nintendo Power table of contents today didn't represent a new look for Cave Story -- it was actually art by Mikael "Orioto" Aguirre, commissioned by Nicalis in honor of the announcement of the DSiWare version of the game. In an email statement, Nicalis confirmed said DSiWare version, saying that "the game is actually DONE, we're currently in final testing internally."
In addition, the long-awaited European version of the WiiWare game (even longer-awaited than the North American version!) is "still scheduled to be released."
Update: Nintendo Life posted three screens, revealing the "classic" Cave Story look, with an added map on the DS's bottom screen.