Actually, it's not a closed door; it's more a door that is opening for people who are already using both Xen Orchestra and Kubernetes.
From a technical point of view, it makes more sense for us to use XO, because its API is easier to use, especially with the new REST API. For the application side itself, it does many thing that we don't have to deal with. For VDIs, perhaps it's not so much. But for other things such as backups, live migrations, templates and VM creation... it's easier. Moreover, using a unique SDK to develop tools makes sense for our small DevOps team in terms of development speed, stability and security.