I'm only familiar with my own schedule and it hurts, believe me (working on game characters since the beginning of this year). I just don't think they can complete a nextgen game of that caliber within such timeframes.
By the time winter 07 rolls around it will have been over two years since ND's last release, and likely longer since they started work on PS3.
Insomniac also didn't just start work on Ratchet when they wrapped Resistance - they had a smaller team working on Ratchet in parallel to Resistance, and then switched people over to Ratchet when Resistance was done. They've grown a lot, they're really a two-project company now. Don't be surprised if the team working on extra Resistance stuff is also looking at early Resistance 2 work. To compare against Resistance, we first saw a glimpse of Resistance in May 2005, with a release in Nov 2006. We first saw a glimpse of Ratchet in March 2006, so a release by the end of 2007 doesn't seem that out of tune with their prior record. Looking at how Resistance came together between E3 06 and its launch, if I had to bet on one company to make their target deadlines, it'd be Insomniac.
Of course, again, a slip is possible in either case. But I don't see it as any more likely than with any other project tbh.