Piper Jaffray's Gene Munster belives that Apple will be focusing on OS X based iPods by Macworld San Francisco 2008.
Munster's belief is likely based on an otherwise overlooked comment by Steve Jobs at Apple's Town Hall which revealed that Apple was working on OS X based iPods:
There is one OS group that does Mac OS X for the Mac and the iPhone, as well as "some iPods we're working on."
Apple uses a version OS X as the basis for the new iPhone, and many have expected a similar widescreen OS X based iPod to come from Apple since the introduction of the iPhone.