Physical containment would work fine. Given the current small footprint of computing modules, we could just run each separate untrusted cloud apps from a node

Physical containment would work fine. Given the current small footprint of computing modules, we could just run each separate untrusted cloud apps from a node the size of a pi0. All we need is a high throughput interconnect with a well defined interface to exchange information. ... wait, that sounds like plan9's dream