FreeBSD unionfs

The BUGS section in [`man mount_unionfs`](https://www.freebsd.org/cgi/man.cgi?mount_unionfs) states:

> THIS FILE SYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK)
> AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM. USE AT YOUR OWN
> RISK. BEWARE OF DOG. SLIPPERY WHEN WET. BATTERIES NOT INCLUDED.

Having a fully working, stable, tested unionfs in FreeBSD would allow the Live ISO experience to be much better, and with way less workaround-ish hackery.