Support for GlusterFS
It would be wonderful if GlusterFS was properly supported, even if only with native CLI tools, which are plenty good for most things. Being able to share local storage between machines as a glusterfs volume or volumes is interesting as a means of building highly-available VMs.
Travis Eddy commented
The only reason I have my larger customers using oVirt.... If XenServer had GlusterFS support for storage I'd switch back. (I still use XenServer for customers that only have 1 vm host)