The GDPR does not count anything as "Personally Identifiable Information", which isn't surprising as that's a US legal term.
What you mean is "Personal Data", and yes IP addresses are considered personal data under the GDPR.
>so deriving an identifier from this for a use case such as analytics would likely require consent.
Consent isn't the only legal basis for processing personal data, though, there are 5 others available.
Only if there is a bijection between the identifier and the IP address, so that you could re-derive the IP address from the identifier. Otherwise, I do not see how the identifier itself would count as PII.
This way of divorcing data from PII by replacing it with pseudonymous identifiers which cannot be linked back is a relatively standard technique for this.
I'm not an expert in this even though I'm a webdev from the EU, so I'm also interested in other people's input.
I don’t believe that one should automatically conclude that just because a cookie requires active consent, any kind of ‘logging’ (local and temporary storage of IPs in order to track website usage) requires active consent. Those are two fundamentally different things.
I’m not saying you should hide the fact that you’re doing it. I’m saying it should be stated in the privacy policy.
Also remember that there is a big difference between ‘personally identifiable information’ and ‘sensitive information’ which are clearly separated concepts in GDPR. Not all collection of data requires active consent.
I did read my EU state’s guideline on GDPR in full, but I’m not an expert. I would suggest reading up on the ePrivacy Directive though, which is still in effect.
However regardless of whether you're using cookies, I still think you need to collect explicit consent as GDPR requires a lawful basis of processing, and I don't see how analytics would fall under any of the other lawful basis's other than consent (_maybe_ legitimate interests?)
If you are using cookies, then my understanding is you need to collect consent where necessary under _both_ ePrivacy and GDPR.
I've only skimmed over the docs, but it looks like they derive a unique identifier from the IP address and user agent which changes every day. IP addresses still count as Personally Identifiable Information under GDPR, so deriving an identifier from this for a use case such as analytics would likely require consent. This is speculation though so I'd be interested to hear what others think.
If it is critical to the operation of the website (functionality like storing saved items in a shopping cart, or security), then you wouldn't need consent.
In reality though, Plausible looks great and using it is a huge improvement over Google Analytics for privacy.