Paleo sustainable at global scale?

As my friends, loved ones and colleagues have probably tired of hearing by now, I've been experimenting since the beginning of October with the paleo diet. In a nutshell, paleo proponents believe that humans evolved over 2+ million years as hunter-gatherers, and only invented agriculture in the last 10,000 years (or is it 30,000? an evolutionary blink, either way), so we haven't had time to adapt, and are healthier eating the "original" human diet.

I won't get into the biochemical pathways responsible or the evidence for or against here (although if you are wondering, I do find paleo very easy to follow and have definitely gotten leaner since starting). The question here is, could 9 billion people sustainably eat paleo in 2050?

The obvious first guess would be no; to get a better back-of-the-envelope, when I have the free time and inclination, I think I'll try to compare productivity of somewhere like Polyface Farms with an industrially produced, grain-based human diet, and post the results here. This of course begs the question of whether Joel Salatin is the right benchmark (it's not realistic to expect the entire world to become enlightened philosopher-farmers, is it?), but it would be a good first step.

In any case, I find the question interesting from both pragmatic and moral perspectives... but until I have a sense of the answer, I am going to stick with paleo myself for all it's worth.