"Then there are the indirect effects, like forcing all IoT stuff to go through a relay server because it's just too difficult to avoid it when everybody is behind three layers of NAT."
I don't have any such issues. Oh, you meant allowing your IoT devices to talk to someone else's server? That might be a problem, but you can work around it. Or, better yet, avoid those sorts of devices. I'm continually baffled by people who are OK with filling their homes with such devices, particularly given that you can accomplish the same things without letting companies spy on you.