That's a pretty interesting technique!
I built a privacy friendly analytics project https://github.com/sheshbabu/freshlytics and I've been wondering how to correctly count unique visitors to a website. I don't store cookies or any PII data at all so by definition, it's hard to distinguish between two different visits - are they from same person or different people?
An alternative approach is used by Simple Analytics - https://docs.simpleanalytics.com/uniques where they use referrer header to derive unique visits. They mention that they don't use IP addresses as they're considered fingerprinting.
But it looks like a hash function (whose salt gets rotated daily) strikes a good balance between fingerprinting while maintaining user privacy. Any downsides to this approach?