The thought of a PDA is a very touchy subject. I think the product more likely to be introduced would be a PDA sized portable VCR-like device. A multi-media player/recorder. Maybe it's not likely, but it's the type of device people seem to be leaning towards.
Not that I think it's going to be introduced in January, or ever for that matter, but I think the PDA idea is dead. If Apple releases anything it's going to have to have features that seperate it from a PDA, even if it shares some functionality. A portable A/V device could be useful for the market that Apple seems to be gearing their computers towards. Not only that, it would be fairly revolutionary.
Their offline-RT codec would allow for 5 hours of video on the iPod so a similar video centric device isn't out of the realm of possibility....