One of the announcements from Citrix Synergy 2011 San Francisco last week was that Citrix was working on a variation of XenClient called "XenClient XT." The XT edition of XenClient is for extra-secure desktop environments where different guest VMs are connected to different networks with different security levels. Prior to XenClient XT, customers had to have multiple physically-separate computers.
XenClient XT is based on XenClient 1.1, although Citrix made several specific security modifications, including breaking the control domain into multiple pieces, and adding support for Security Enhanced Linux (SELinux) guests and security policies. Watch Gabe Knuth's quick interview: