Xen? Oh please
You can't really blame Red Hat for getting rid of Xen. Xen was a mess to maintain. Try patching your kernel manually and you'll find that running Xen means that you have to stick with specific kernels and is a pain. Xen also never made it to the kernel for this reason. KVM is a lot more agile + development is progressing a lot faster. KVM, VMware and possibly Microsoft's virtualization solutions are the future.