I am not sure if the use-case here is to track people that delete their cookies or if the author found it easier than using simple UUID stored in cookies.
hash(salt + ip_address + user_agent + some_other_unique_characteristics)
for analytics you could rotate the salt daily if you're only concerned about daily unique visitors
One thing I'd like to do is try something like what you said server-side and compare how closely a hash of those properties matches the "accuracy" of fingerprinting. I'm only looking for something of reasonable precision during short periods of time (to avoid obvious double-counting) so if that tracked reasonably enough, it'd be a very interesting alternative.
That way, you can only track any given visitor for max 24 hours, which often would mean tracking them across a single "visit". I'm pretty privacy conscious, but personally would be absolutely OK with this.
> However, GA has grown exceedingly complicated, installs cookies (thus requiring the utterly annoying cookie warning in the EU)