Great question.
Our thinking is that we want to build Docker for X using the best and most native hypervisor available on X. For Windows 10 (non-Home), we currently believe that’s Hyper-V. If we decide to support other Windows versions, we’ll look at what virtualization tech is going to get our users the best experience on those versions.
We’re not going to rule anything out, but I think we’re unlikely to make the local hypervisor plugable if that means that the user experience becomes more variable or unpredictable (this is arguable the case currently with docker-machine where different drivers implement filesharing, networking and other features differently, or not at all).