Gerd Hoffmann of Red Hat has commented on the current upstream state of GVT-G. With Linux 4.10, there is virtual GPU support via Intel's Graphics Virtualization Technology for Broadwell hardware and newer and it will work without any extra QEMU patches. However, currently it's limited to headless operation, so you won't get any native display support so just useful if you want to do compute with say Beignet or using x11vnc for remote display access.
The display support for GVT still requires more changes to the Linux kernel that didn't make it for the 4.10 cycle. There will also be some QEMU patches needed too for the virtual display support.
Those are for host requirements while Linux guests will need at least the Linux 4.8 kernel, but there may be some kernel releases not yet quite compatible.
This state of GVT was shared this weekend on igvt-g. Those wishing to learn more about the Intel Graphics Virtualization Tech can visit the project site at 01.org.