Doesn’t this mean that if you accidentally serve your website on two domains (e.g. example.com and example.net with no redirect) it will count one visitor twice if they visit both domains? What is the benefit to including the domain in the hash?

Not really keen on the use of the IP address. I’ve been behind load balancing proxies and weird mobile networks often enough to know that I can appear from a dozen different IPs in the space of an hour just by browsing the web normally with default settings.

Have you considered requesting a 24 hour private cacheable resource and counting the requests on the server? Or is the browser cache too unreliable?