It's wrong to think of Pickle as a theme. As was mentioned, it's a SAAS solution but because it's also available as a self-hosted platform, it's going to be labeled as either a theme or a plugin. Jason isn't the first to do this; Studiopress offers New Rainmaker as a SAAS platform. The admin is simplified and very customized, the feature choices are limited and there's no provision for adding additional plugins. Both are solutions for a specific audience. Splitting Pickle into a theme and a plugin would add additional complexity that goes against the goal he's after - simplifying the admin UI and setup UX for the average Joe Restauranteur.

Frankly, I also see a need for these niche-specific solutions. I've been working on one myself, and I'll be buying Pickle to take it apart so I can learn how Jason approached solving the common setup/data entry challenges new users always have questions about.