[beardog]

It can be used to track you across the web, get a general geographic area, and if you have the right connections one can get the ISP subscriber address. Given that PII is anything that can be used to identify a person, I think it qualifies despite it being difficult for a rando to tie an IP to a person.

Additionally in the case of ipv6 it can be tied to a specific device more often. One cannot rely on ipv6 privacy extensions to sufficiently help there.

[rtsil]

That's compounded by the increasing use of static IPs, or at least extremely long-lasting dynamic IPs in some ISPs.

[TylerE]

There is a reason I specified ipv4 and not v6