I am a complete noob with Xen, although I've been a VirtualBox user for a decade. I was given a project at work and Xen was suggested as a solution. I worked through Fedora 28 (no joy), Debian 9.5.0 (workie but clunky), XenServer (a sledgehammer to kill a gnat and the giant does not want to let go), and then found XCP-ng...
Still getting my brain wrapped around the possibilities.
The vGPU feature is near and dear to my heart. I have release-vs-hardware issues with GPUs all of the time and this looks like it might be a way to be more productive in my troubleshooting. Haven't shot anything yet, but looking forward to it.