You can do that with the privacy extensions. Plus on IPv6 you should get enough address space that it makes no sense to run a scan against anyone.
On IPv4 or NAT there's just 65535 ports to check. On a /48 with privacy extensions there's 2^80 addresses to go through, which from an external point of view don't remain constant. You can't even ping all of that.
As a end user, my inbound ports are all closed, and I don't care about scanning. But I don't see why everyone should be able to differentiate traffic from my phone from traffic from my laptop so I'm happy that they use the same public IP to connect outside.
Have you ever heard of TCP/IP stack fingerprinting? It is very likely that someone intercepting your traffic can tell apart your phone and your laptop regardless of the originating IP address. Odds are they can even tell your operating systems.
It's not because someone can say whether I'm at home or not by looking at the lights that putting a plate in front of my home saying whether I'm here or not is a good idea ^^ (sorry for the poor metaphor;) )
