I like the idea and I agree that this will be the way of the future, but it just doesn't seem practical at the moment. Portability is hamstrung by the need for a constant network connection to accomplish anything, and the cost savings of a Chromebook are almost completely washed out when you factor in at least $20/mo. for Linode.
Why not just get something from System76? Or install whatever OS you like on one of the notoriously Linux friendly Lenovo laptops? You end up with better hardware specs, more flexibility, and comparable portability for the same price.