The new Raspberry Pi is seemingly quite capable of being a thin client, that is if you combine it with ThinLinx.
Just buying the new Raspberry Pi won't cut it though. The Citrix Receiver need to work too. That's why Citrix has worked with the Pi organisation and with with the release of XenDesktop/XenApp 7.6 FP3 and the new HDX Thinwire compatibility codec, Citrix also has a codec that would perform efficiently on the Pi2 without the need for hardware accelerated plugins. ThinLinx offers a supported operating system, complete with HDX hardware acceleration support and management software.
The ThinLinx OS costs $15 per endpoint and as such more than the hardware but it still makes for an interesting proposition at a total of $50 per device.
Of course the Pi has hidden costs: keyboards, pointing devices, SD cards, WiFi dongles, USB hubs and monitors aren't free. But dedicated thin clients also require those devices before being useful, making a Pi an interesting VDI option. And then there's the management cost. How are you going to handle a new version of the Receiver orf a configuration change? Some say Android is a better choice because Android MDM/MAM is included in most desktop virtualization bundles.