Knative is really an alpha piece of software at version 0.2.2 for the serving component. Riff is also at 0.2.0. What do Pivotal plan to do if both implement breaking changes (extremely likely), maintain a fork?
The other issue is what value is this all really providing? Kubernetes provides a standard API that abstracts infrastructure and deployments.
The benefit that Lambda brings is very simply connecting together cloud services. None of these FaaS on Kubernetes products do that. For anyone interested I looked into the current landscape on Kubernetes and gave up since it's all pretty worthless. https://kubedex.com/serverless/