SmartOS is illumos distribution, designing as hypervisor os.
SmartOS has multiple separate mechanism, Zone and bhyve.
Vms run on bhyve, bhyve are separate by Zone, SmartOS use VMs separate by two layer.
Can user use SmartOS as lightweight version of Qubes os?
Qubes os uses Xen, Linux hypervisor is KVM, bhyve on Smart OS is third choice for user!
Proxmox repository has FireFox and Chromium, if user installs web browser in root or user account by apt install command, so user can access to Web UI from itself account.
This approach is as if dom0 of Xen, so user can use Proxmox as desktop OS.
SmartOS has too great Web UI, but there is not web browser in pkgsrc of SmartOS, so user cannot access to Web UI from itself.
If web browser adds pkgsrc of SmartOS repository, user can use SmartOS as desktop OS.
How would it be different from using a GUI hypervisor (virtualbox, virt-manager, hyper-v, whatever) on Windows / a linux distro?
Illumos is nice, but the project lost the traction it had back in OpenSolaris days (it was an amazing OS!) when Sun got bought by Oracle. Now it’s pretty difficult to find consumer hardware that works correctly with Illumos I’m not sure the whole OS and zones are well maintained either.
SmartOS is designed hypervisor OS, it is as if Proxmox.
And VMs are separation by two layer, Zone and bhyve.
VMs run on bhyve, bhyve runs on zone, this model is more secure than Proxmox.
And SmartOS uses bhyve for virtualization, user can choice difference hypervisor as Xen and KVM.
And SmartOS is developed by Sumsung, so project has continuity!
Solaris and illumos has Zone, Zone is like Docker of Linux.
Zones are separate other Zones, so this is very secure.
And bhyve can run in Zone, many OS can run in Zone.
In this model, VMs are separation by two layer, Zone and bhyve.
This structure is like Xen, bhyve in Zone is safer than KVM or Docker.
And SmartOS is developing by Sumsung, so illumos has continuity.
So SmartOS is lightweight Qubes os.