Well I think the appeal to these type of ideas is more decentralization than profit. I doubt I'll ever even get my money back on my s9s (partly because I keep giving them away so other people can do this), but if we get to the point where every HVAC on the planet is hooked up to a miner, we're more decentralized than ever. I admit, that's a hyperbolic scenario, but even an eighth of the HVACs on the planet vs. attack entity X would be a pretty stacked (pun intended) fight.