A British TV celebrity hints at the possibility.
A Twitter conversation between British television celebrity Jonathan Ross and a follower may have inadvertantly leaked the announcement of a new Metroid game for the Nintendo 3DS, to be revealed during Wednesday's press event for the system.
Ross announced that he would be part of the European press event this coming week, and briefly discussed how much he liked the 3D effects of the handheld. Followers then began asking him about the event and what might be unveiled, with one mentioning that he was going to "keep his fingers crossed for Metroid". To this Ross responded: "I think you're going to be pleased then...", without offering any further details.
Does this mean a 3DS Metroid game will be announced? Nobody knows, but it's safe to assume that, as a celebrity involved with the planning of the event, Ross is at least partially aware of what's going to be shown to the European press.
The European 3DS press reveal is scheduled for Wednesday, January 19, with a 3DS preview event being held in New York City on the same day.
UPDATE: In a follow-up posting Ross stated "A few other faves coming as well - plus a few unexpected revivals!! Can say no more, sorry."
UPDATE 2: Ross confirms that he was not referring to a Metroid title, but rather the general games list.