Once the backup and snapshotting framework for Xen is put in place by the Xen community, and as the market share of Xen continues to grow, it will get put onto our roadmap.
I think that the marketshare might be larger than you imagine. Xen is used pretty heavily, often by people who don't realize that they are using it.
I doubt that those features will ever exist because they kind of go against the ideology of the community. They might, but I don't see it happening since the functionality already exists, just not via an API. It would be great to see as it would make the product a lot easier to use. But seems unlikely, especially as the product is so mature and the XCP project implemented them in its own way indicating that there is no interest in doing it at the Xen level.