At MailPace we already enforce DKIM, it’s pretty basic stuff. But list-unsubscribe is optional for our senders.
We can make this a requirement and manage lists for senders who don’t / can’t implement a webhook to handle it (we already default to blocking resends to emails that hard bounce).
However I am curious how Google will track this. Just because the header is set, it doesn’t mean it’ll do anything. In fact it can be used by spammers to identify legit email addresses and spam them separately.