There's a hidden capability in Citrix XenClient Enterprise you might not know about -- the ability to turn old PCs into thin clients.
XenClient comes with XenDesktop Enterprise, which means if you have Enterprise or Platinum, you're already entitled to use XenClient Enterprise on your desktops. I recently uncovered an article by Citrix's Sham Sao about using XenClient to repurpose PCs as thin clients. At first, I thought he was talking about the whitewashing aspect of client hypervisors that allows you to deploy a single image to every desktop because the hypervisor itself handles all the different hardware under the hood.
This seems like a viable solution that could be right under your nose.
Methods for repurposing PCs
To pull that whitewashing method off, you'd be wise to have a tightly controlled image that refreshed at every boot. Since you probably moved to virtual desktop infrastructure (VDI) to get away from Windows on the desktop and didn't intend on doubling the number of desktops you have to manage, this might not sound like the greatest idea in the world. Nonetheless, plenty of organizations repurpose old PCs as thin clients, and it is helpful to have a single image that can be tightly managed, running on a hypervisor that can also be tightly controlled.
Instead of Windows, you could run a solution such as Stratodesk in the virtual machine (VM). Stratodesk has a tool called NoTouch that allows you to deploy a thin client OS to any Intel-based device -- even thin clients from different vendors (including Apple). You're then able to manage them all from one interface, and your users have the same thin client interface from wherever they log on.
You could also run Linux inside the VM, but before you go down that road, let me save you a step.
Using XenClient to create thin clients
XenClient itself has a built-in Citrix Receiver, which came from Citrix's acquisition of Virtual Computer. (In fact, most of XenClient Enterprise is a direct result of that acquisition.) A service VM acts as the interface to all the other VMs, as well as the interface to configure hardware in XenClient. This VM runs Linux and has a built-in browser, Remote Desktop Protocol client and Citrix Receiver for Linux. In other words, you can use Citrix XenClient Enterprise without any VMs as a secure, manageable thin client.
What's more, if you have hardware that can run Windows and was previously purchased with a Microsoft Software Assurance license, you do not need to purchase a Microsoft Virtual Desktop Access license to access a Windows virtual desktop. (Well, as long as that's your interpretation of the rules. I've heard conflicting stories, but what else is new?)
More on thin clients
Comparing thin vs. thick vs. zero clients
Considering Android thin client devices
Tools for converting PCs to thin clients
That means if you run XenDesktop Enterprise or Platinum and your endpoints have Software Assurance, you now have a no-cost PC-to-thin-client conversion tool at hand. Simply install XenClient on the endpoint, point it toward your Web interface or storefront URL, and you're all set.
I don't know anyone who uses this in production, but I know they are out there. I verified that the functionality in Citrix XenClient Enterprise exists, but beyond that, I don't know how the day-to-day experience of using the built-in Citrix Receiver for Linux is. Nonetheless, if you already have the tools at your disposal, it's worth a shot to see if it will work in your environment.
If you have information on performance and user experience, please share it. On the surface, at least, this seems like a viable solution that could be right under your nose.