Hypervisor.framework would need to support it as well, not sure if it does. It just in 10.11.5 got better support for USB.
Veertu has graphics support, so H.framework must support it already.
That's not really true. It has all of the primitives you need to support PCI graphics devices (or even memory-scraping legacy VGA if you hate yourself). It had all of the primitives you need to do emulated USB on 10.10 -- passthrough is a different matter.
For implementing GOP you need to support UEFI, generally, but beyond that it's just supporting another UEFI protocol.
Hypervisor.framework itself only deals with CPU virtualization and is agnostic to whatever device model is implemented in userspace.