There has been some recent blog discussions about the next feature set for the Xen.org community hypervisor. The feature list at http://www.xen.org/download/roadmap.html is a collection of “wants” gathered from the general community and is not a definitive roadmap. The Xen hypervisor developers monitor this list when determining what features to work on, but as with any open source project – there is no guarantee that a given feature will be developed.
Also, the plan to move the next version from 3.4 to 4.0 instead of 3.5 is based on the change of the underlying Linux kernel for Dom0.