So how do you prevent these from becoming ovens if you don't add exterior cladding? Seems to me that container houses are a fad and likely won't stay around very long. Too many unknowns.

Supertherm.... Ceramic paint that has hi-performance insulation properties at a thin application. You can also add insulation to the interior to double the benefit. There really aren't that many unknowns. Its all a matter of building commissions only wanting to do what they are familiar with, thinking that something they don't know about can't be safe.

You know there's an article series started on this topic right? Why don't you read and learn more?

Look Here