When we started the Virt SIG, our stated goal was to support one recent version of Xen with a recent kernel. We updated at that time to Xen 4.4, as the most recent stable release. We skipped 4.5; but now with 4.6 out, I think it's about time to upgrade.
Moving to 4.6 has several distinct advantages for CentOS 7. Xen 4.4 has no systemd integration, while Xen 4.6 does. Additionally, Xen 4.4 has an insufficient level of ARM support, while Xen 4.6 does.
The Xen releases are heavily tested upstream, not only by the open-source team, but by the vendors who build their products on Xen. I'm fairly confident that moving forward to Xen 4.6 should be a relatively safe maneuver for most people.
So I shall be moving towards releasing Xen 4.6 for CentOS 6 in the not too distant future.
That said, the Virt SIG is a community effort -- if anyone in the community wants to step up and maintain the Xen 4.4 packages within the SIG, they would be welcome to do so. The burden of doing the maintenance should not be too high.
Security updates will continue for 4.4 until the 4.6 packages are fully ready (and may continue for a month or two afterwards, depending on severity, to provide a transition period).
-George