That's not the case - there's only one virtual machine shared by all containers.
Oh...that's interesting. That would even be useful on Linux to enable greater resource separation between processes...say being able to lock all Docker processes down to 1-2 cores on a machine and with a hard memory limit they can't exceed.
That's already possible with cgroups. Adding a virtualization layer even on Linux would be wasteful, since Docker runs natively on Linux anyway.
What you mention is a major reason why Linux containers were invented, and is already possible with Docker today. Take a look at the '--mem-limit' or '--cpu-shares' flags for 'docker run', for instance.
I would bet money that it does not. The Virtualbox based solutions all create one VM and run all containers there -- why would they stop doing that just because they're using a different means of virtualization?
Well part of me hoped this was actually Docker for Mac, not just running Docker inside a Linux VM.
Guess what? I can do that on Windows 10 too and it works like a charm.