Silicon Alley Insider has it from a "plugged-in source in the mobile industry" that Apple will demo their tablet in January, and have asked selected iPhone devs to prepare high-res apps for the occasion. So, what exactly is the occasion?
The first possibility—and the one that could put a welcome end to the endless fragments of tablet information that we've been parsing for the last few months (fuck that, years)—is that this is some kind of public demo. Apple's iPod and iPhone events have been dominated by apps since the App Store opened, sometime to a fault. If Apple's going to announce this thing, they're going to have app support.
The second possibility—the more likely one—is that this will be a closed demo; that it's some kind of private event to give app developers a heads-up before a public announcement, and presumably to comfort them about app interoperability between the iPhone and the new tablet device. According to SIA's source:
[Apple has]told select developers that as long as they build their apps to support full screen resolution — rather than a fixed 320x480 — their apps should run just fine
Essentially, it sounds like they're asking app devs to write quick'n'dirty fixes to remove specific resolution limits from their apps, so that they can run—though not necessarily gracefully—on a larger screen. That's the kind of thing that could put developers' fears at rest, but not the kind of thing that Apple would want to show the public.
The source claims the device isn't going on sale until later, which fits nicely with the WSJ's claim of a March release date, which falls roughly in sync with announcement-but-no-product Apple events of the past. Also, the source claims that the entire Apple tablet concept is a sick prank by Steve Jobs, and that he literally hasn't stopped laughing for, like, three whole years. [Silicon Alley Insider]