This is a way to deploy and manage a stateless web application ("function") without needing to get into a bunch of low-level details, and get closer to pay-for-what-you-use.
Billing models do in fact affect our design discussions and we're still kicking the questions around[0][1].
How though, won't you need a Kubernetes cluster running?
For cloud providers the boundary is likely to become execution-seconds. As Kubernetes worker nodes become abstracted away this will be the remaining way to track utilisation.