Tom's Hardware is pointing to an Nvidia source that confirmed Apple was the first to receive Ion test units, and said that Apple most certainly had an Ion-powered Mac Mini in the pipe. Apple Insider is more inclined to believe it's for the Apple TV, since a move to Atom would be a step up from its aging 1GHz Intel Crofton proc.
Both products make the most sense for a low-power, low-cost processor, but a dual-core Atom 330 running at 1.6 GHz would certainly be a step down from the Mini's current Core 2 Duo at 1.83 and 2 GHz, so I would place my chips in the Apple TV stack. The Nvidia 9400M would bring a nice boost to the Mini's paltry HD video capabilities however, and OS X config file snooping has turned up evidence for a 9400M-powered Mini recently (doesn't mean it will also use an Atom processor).
Or maybe they'll simply combine these two fairly confused product lines into one dimunitive full OS X machine (please) that's perfect for the living room. Tom's source says the new Ion-powered product will hit around March. We'll see about that. [Tom's Hardware, Apple Insider]