I started my experimentation with virtualization back in 2008. and back then I started with  Xen. It was the virtualization option that OpenSuSe 11.1 had built in, then in 2009 I switched to Xen Server as a dedicated hypervisor to gain the clever GUI for managing the VMs.
A couple of years later I decided that Xen Server wasn’t meeting some needs, mainly because most pre-made disk images were only made for VMWare’s ESXi platform and very few were available for Xen.
In 2011 I switched to ESXi 5.1. Ever since then, I’ve ran a handful of VMs, but looking back I really wasn’t taking advantage of the capabilies of ESXi. Even now I’m not. However I’ve been stuck using it (in Dec 2015 switched to ESXi 6.0) because it was all I knew to get virtual environments set up.

On the flip side, the NAS software I’ve been using (UnRAID) has had some major changes added in the last year with their release of version 6.x. The new version brings virtualization using KVM/QEMU to the software suite along with Docker containers.
First off Docker containers are marvelous. They make using and managing different software a breeze. Software which I would have created a new VM for (and had to maintain), is now one package that is fully configured and just works. No more having to make a custom Linux install to run a music server and another for torrents, etc. Each container runs inside it’s own memory space, so one crash doesn’t take down all the other containers (the reason I would have in the past created a new VM for each installation).
With docker containers and the slick interface that UnRAID has given this technology, I’m sold on exclusively using containers. If I need a custom VM (like windows or pfsense or something else specialized) I can still create a VM and run it under UnRAID.

Between the capability of Docker and KVM/QEMU virtualization options in UnRAID I am questioning the need to run Xen Server or ESXi when everything I would need is already covered by UnRAID.

The reason I’m writing and thinking about this is because currently ESXi is giving me grief because I can’t pass through nVidia GPUs (unless they are Quadro or Tesla series) to guest VMs. This prompted me to think about switching to the latest XenServer since I don’t think it has this imposed limitation.
Then I stopped to think about what are REALLY my virtualization needs.
Would UnRAID be a sufficient solution?

I think so, considering that I am currently running UnRAID as a guest on an ESXi server along with 2 Windows VMs and one linux vm. UnRAID does file management and storege server duties, along with a bunch of docker images.
Moving everything to a system with UnRAID as the host, would change very little, and I don’t have to maintain ESXi or other enterprise grade hypervisor. Going back to the basics as they say.