I too have just discovered qubes, and it looks like exactly what I’ve been looking for, with one exception. I really neeeeed GPU passthrough to a windows VM. (I can’t see shutting things down all the time to dual boot, that’s just too horrible.)
I don’t really understand what the problem is; Xen supports it now, if I’m reading all those pages correctly, pretty much any monitor now has at least two physical inputs (I’d run separate cables for system video and the gpu card and push the input button on the monitor), if I had to install a separate usb card for the sole use of the passthrough VM and KVM switch the keyboard and mouse, I could live with that. All dom0 would have to do with that VM would be start/pause/stop it, no other emulation or other interaction would be needed.
I’ll add I stumbled across qubes in conversation while asking questions to try to figure out which linux/xen distro would be the easiest to bring up: the learning curve on all the howto pages seems quite daunting. It seems sad to have to choose between qubes (which does in a polished way what I had in mind) and roll your own linux/xen, simply beacuse qubes, built on xen, won’t use a facility that already exists in xen. I really don’t understand what the problem is.