Careful, you have to also add --no-preserve-root to make sure you get all of it out. If you leave the roots, it'll just grow back later!
(But seriously, don't actually do this unless you're prepared to lose data and potentially even brick your computer. Don't even try it on a VM or a computer you're planning to wipe anyway, because if something is mounted that you don't expect, you'll wipe that too. On older Linux kernels, EFI variables were mounted as writable, so running rm -rf / could actually brick your computer. This shouldn't still be the case, but I wouldn't test it, myself.)
Can I pick a PC? x86 is retro, right? /joke
But seriously, probably the PS2. Mainly because it's the only console I got as a kid and also because it's the last console before games and consoles started wanting to phone home over the Internet. I have PS3 games that I'm pretty sure are permanently hampered or unplayable because their servers are offline, but I feel confident I can still boot any PS2 game I own and play it without issues.