Android 3.0, aka Honeycomb, has been pushed by Google and Motorola as a tablet-centric version of the Android OS. Google is open about their plans to unify Android and we may in the midst of a stirring towards that now. While Honeycomb's default setting is 1280x768, it switches into a different mode when you change the screen setting to WVGA.
This setting includes the basic framework for a Honeycomb smartphone. It isn't proof positive that Google plans to unify the two systems just yet, but it is evidence that they've toyed with the idea. We've also heard rumors that the next mobile version of Android will be 2.4 "Ice Cream Sandwich". So really, anything is possible at this point.
Handset Honeycomb (as I'm calling it) uses a more traditional, non-tabbed Android browser and also goes back to the old style of unlock screen. The status bar is more smartphone focused and the homescreen is notably more sparse. There's a lot less battery life and processor power to play around with on most smartphones.
Here's one possibility I haven't heard yet: What if this is the bare-bones of some sort of plan for the Atrix? If Honeycomb can switch between a large display mode and a WVGA mode, maybe the Atrix is meant to (eventually) run a stripped-down version of 3.0 in handset mode, and a full version of Honeycomb in notebook mode?
Beyond the Atrix, Google could be laying the groundwork for a generation of handsets that dock with full-on PCs and notebooks in a similar manner.