it seems to me to be good to stay diversified, and by keeping an x 86 development project going, Apple may be reducing any risk factors associated with sticking with the PowerPC.
The issues regarding Cocoa vs Carbon do seem interesting. Notably, Apple has always put a big emphasis on Cocoa. Maybe this is one reason. Considering Cocoa has its roots way back in NeXT (which as Rigor pointed out, ran on several architectures), the link seems more than coincidental.
With respect to the idea that Apple would release this only if it was on its death bed, well, I am not so sure about that. For instance, no respectable developer would spend a fortune recompiling their apps to run on a platform that was about to go wayward. Again, if Apple was down for the count, I doubt it would want to spend the massive amounts it would take to finalise and then market this product to the windows Calvinists [think of all the additional device drivers, code optimisations etc that would have to be undertaken just to make it useable. Even on Mac related hardware we are still awaiting the arrival of some driver related support]
Finally, with respect to Nick de Plume, I have found that in the murky world of apple related rumours, the info he has published in the past tends to be quite reliable. Now, the guys at MOSR on the other hand...