The WikiHouse chassis system [pdf]

The difficulty with building systems is reflected in the first section...foundations must left as an exercise for the reader. It means getting started is outside the scope of the system and requires traditional localized approaches.

There's no universal foundation. Each one is site specific and requires specific local knowledge. Generally, building one of these systems is going to be harder because it requires the foundation contractor to provide a custom interface to the super-structure (two parallel beams in this case) rather than one of the local norms.

Stepping outside of local norms reduces the available trade base, increases the likelihood of error, and usually increases costs (smaller trade base, increased complexity, increased risk).

To put it another way, getting the foundation built is not only non-trivial, it's the most uncertain portion of the building process (until you dig, you don't know what's buried) and the most critical to producing a sound structure.