https://www.qubes-os.org/ uses Xen and there was interest in supporting openSUSE as guest or even dom0 - see https://build.opensuse.org/project/show/home:marmarek:QubesOS for the PoC of getting the tooling to build.

Just one clarification: running as a HVM guest (i.e. fully virtualized) or a PVH guest (using hardware virtualization features) under Xen would still work. For the guest side only running as a PV guest (paravirtualized) would no longer be possible.

https://www.qubes-os.org/faq/ says

By default, Qubes uses Xen’s PVH and HVM virtualization modes, which require VT-x/AMD-V.

Xen domU support should be retained so that openSUSE can continue to be used in XCP-ng, XenServer, Qubes, and other platforms that use the Xen hypervisor.

Keeping open to not forget about release notes entry.