Well, since they say that the PS3 is on a 10-year life-cycle, you'll be waiting a while, while I can see Nintendo announcing their next plans any day now. My prediction has been that Nintendo's not sweating Natal and Move because they've got something special up their sleeve, which will only be revealed at the opportune moment, when the time is perfectly right.
Point being, if you're waiting for Sony's next console to hit shelves before you decide to buy a next-gen console, you might be watching Nintendo and Microsoft's next child for a year or five before you get a taste of the next generation.
my only regret... is that I have.. bone-itis. I'm with Coco