Nested Virtualization

Expose Intel-VT extenstions to guest OS.
Hyper-V nests only Hyper-V.
Does not allow VirtualBox or any other 3rd party virtualization app.

# Expose VT Extensions
Set-VMProcessor -VMName $VMName -ExposeVirtualizationExtensions $true
# MAC Spoofing (Networking with Nested VMs)
Get-VMNetworkAdapter -VMName $VMName | Set-VMNetworkAdapter -MacAddressSpoofing On

App @ VM on VirtualBox on Linux (Vagrant's popular ubuntu/trusty64 box, which requires VirtualBox as the provider.
Hyper-V and VirtualBox are mutually exclusive hypervisors; cannot co-exist on one Win-OS, so would be a work-around.

VM-based-app:     Vagrant|Minikube|...
                     -----------
Type-2 Hypervisor:    VirtualBox
                       -------
OS @ VM @ Hyper-V:   Linux Guest
                       -------
Type-1 Hypervisor:     Hyper-V