Launching it as the next 360 would make sense since they have already achieved a beachhead with the first few SKUs among hardcore gamers. Usually it's difficult, but I think Natal may provide enough differentiator and attraction to make the leap to casual gamers. e.g., use it for shopping measurement for eCommerce
For Sony, they have a small window to position themselves properly. I don't think Microsoft will let them be though. We may see more active MS marketing at the very beginning of 2010 since more of their titles will be ready compared to 2009.
If Sony wants to, the new controller can be a totally separate platform (e.g., games/applications can run on the stick alone without the TV using the right h/w plugin). Because of the plugin patent, it can also be seen as a h/w, s/w, protocol standards for interfacing with existing digital equipments (Lego MindStorm, electronic stuffed toys, musical instruments, ...) and sensors (Vitality sensors and trackers for babies and pets). Or just a video game controller.
Regardless of what they do, applications/games, user experience and marketing are still the critical success factors. They are getting better, but still fumbling in these areas, and not punchy/sharp enough to penetrate through all the noises (Some small, tactical efforts and missed opportunities). As an organization, I think Sony performs best when pushing an industry standard (a la Blu-ray). Perhaps, they should also consider working with well known consumer brands to push the concept.
EDIT: They may not want to push it via the usual standards route. It's too time consuming. An express route is needed, like how OpenCL was established relatively quickly.