Red Hat supports Xen until 2015 (I think it was), and based on the number of important customers they have there still uses Xen, they will either stop or continue to support Xen.
But KVM is very cool from a developers stand point. All feaures that are in the kernel, are also in the guest. For free
Xen is not like that. You have to modify the feature that you want in the guest.
But Solid ICE, is really something nobody besides Red Hat can offer. So mayby VMware is not afraid of KVM compared to Xen, but they might be about Solid ICE.