There has been a very (welcomed) recent addition to the Microsoft Open Interoperability Program, in particular, the ‘Infrastructure’ section.

Citrix VDI is now supported by Microsoft (and Citrix) in a Lync 2013 environment!

http://technet.microsoft.com/en-us/lync/gg131938

Citrix VDI now listed and supported by Microsoft

I have many clients that have held back on Lync due to the lack of Microsoft support for Citrix deployments, so this is definitely been an overdue requirement.