I am unaware of any current Xen support or plans to support it in the future. Redhat have already announced they are deprecating Xen and future RHEL versions will be built around KVM (see here), so it would seem to be rather short sighted to expend development effort on supporting a virtualisation system that is in decline.
This is an old thread, but still relevant. I think the above is all wrong, because:
Redhat is only 1 of many distributions, and not the most popular one either!
Redhat bought Qumranet some years ago and started to build their virtualisation solution around qemu/kvm. This was a strategic step and has nothing to do with Xen being relevant or not. The result is that today Redhat is able to compete with VMware and Citrix/Xen in the virtualisation arena.
KVM is the newcomer, Xen and VMware are the established solutions. Just have a look at what the big guys are using - AWS, etc.