What if you had one-day retention of IP addresses for per-day unique views? Seems like too important of a metric to eliminate completely, and one-day retention seems like a decent trade-off at the expense of being able to do unique analysis over longer time periods.
One can use hashes with regularly changing salts that are destroyed after a while to make older hashes unusable though for some purposes.
But to my eyes, expiring salts isn't much different than deleting ip addresses after one day. Just more machinery. People have to trust that you're doing either, so why bother beyond being able to use the word "hashing" in marketing language?
That doesn't provide any practical amount of privacy. For a longer discussion of why this is at best a placebo, see: https://news.ycombinator.com/item?id=17170468