All for Kubernetes.
edit: links fix
Just from my perspective, having sat down and done a hackfest with guys from Deis in Redmond, they bring a phenomenal amount of experience in Kubernetes to Microsoft. We have a number of people that work in the area (contributing helm charts, other Pos, etc), but more knowledge in an interesting and growing area is always great to have.
Additionally, Workflow is a great way to get started on containerized apps and it works quite well atop ACS.
If people are doing interesting things on Azure (ACS/acs-engine or even VMs) using Kubernetes or DCOS, I'd love to hear about it.
Because they're selling time on an IaaS. They don't have to pick winners when they present a fungible pool of resources.
By way of analogy, BP and Shell don't care where their petrol gets burnt. Ford, GM, it's all the same to them.
Disclosure: I work on such a platform, Cloud Foundry, on behalf of Pivotal. We have a close working relationship with both Microsoft and Google.
So it is Kubernetes AND Mesos for them.