The big problem with trying to limp through another couple of years with the PS2 is the lack of online, lack of built in storage, and the fact that Sony would have essentially been conceding the HD film market to the HD-DVD camp.
I think it would have been more beneficial to do the opposite of what you're suggesting, and launched a year earlier. The PS3 should have compromised a feature somewhere, whether it was the pursuit of Cell, Blu-Ray, or both, and just gotten the thing out the door with a $399 target ASAP.
HDMI, a year lead-in demonstrating PSP-to-PS3 interconnectivity, and a lower price point probably would have been enough to begin drafting a eulogy for Nintendo, as I think it absolutely would've changed the fortunes of both the PS3 vs the Wii, and the PSP vs the DS.
Blu-Ray could've then been presented as an optional accessory for this past Christmas, after the PS3 already had a 10-15M install base. Bundle one of the 'big' games like Motorstorm with it as an incentive to buy, and it'sGame Over, Sony FTW.