Right now, only Xen, KVM and EC2 HVM are supported hypervisors. Hopefully an OSX might come with vmware support later.
Instead of having an full OS-like isolated system within a single OS without virtualization, this is using virtualization but avoids having a full OS-like system inside the guests.
If you have OSv working both under virtualbox or vmware on your OSX dev box and under KVM or EC2 HVM on your cloud production environment, then it might be possible to have a docker.io features directly under your OSX dev box.
Also, if you're willing to virtualize something, and want Docker features, why wouldn't you virtualize Docker?
Currently if you want to use docker under OSX you have to run it inside a Linux VM (typically using the vagrant / virtualbox). But the Linux VM is using a bunch of memory on your dev environment. If docker could run the app inside virtualbox + OSv rather than having to use virtualbox + full linux + LXC I assume you would get a more lightweight dev environment (faster boot times and less memory usage).
Wouldn't it be possible to run a minimal POSIX OS inside a container? (genuine question, I don't know the answer to)