Linux

Might be possible? It's not only possible but rather easy to do, in fact I often have multiple installs side by side in different subvolumes and I can switch between them, reinstall as needed, snapshot them. The only partition I have separate is /boot because it has to be vfat for the esp. Tbh accidentally blowing up a subvolume isn't all that much more or less difficult to do than accidentally blowing up a partition. IMO if you're paranoid about wrecking something the only safe separation is multiple drives and disconnecting the one you want to avoid touching.