The domain capabilities XML needs to be extended to handle conditional enums. Dan outlined a schema here: http://www.redhat.com/archives/libvir-list/2016-May/msg00575.html http://www.redhat.com/archives/libvir-list/2016-May/msg00624.html http://www.redhat.com/archives/libvir-list/2016-May/msg00669.html This will be needed if we want to expose things like graphics type=spice GL support, or controller type=usb models. I don't know if there's any truly pressing need at the moment, but this work may need to be prioritized in the future if any new feature becomes dependent on domcaps
*** Bug 1337740 has been marked as a duplicate of this bug. ***
Adding conditional logic in the capabilities is quite a large burden to support and there's no sign of people wanting todo the work, so closing this RFE for now.