Seconded. Been daily driving it on ThinkPads now for something like two years. I will never go back, and one of the few things which might draw me off Qubes OS is if OpenBSD cleanroom reimplemented Qubes OS with their own OS and hypervisor. (OpenBSD because nobody beats their long term code quality and consistency.)
OpenBSD can run as a Xen guest, so it should work as a QubesOS VM.
Not OpenBSD but FreeBSD: https://github.com/BawdyAnarchist/quBSD
> quBSD is a FreeBSD jails/bhyve wrapper which implements a Qubes inspired containerization schema. Written in shell, based on zfs, and uses the underlying FreeBSD tools.
Not saying it'll do what you want, but the idea is out there...