This looks really nice, but what’s to stop it getting blocked like all the other trackers once apple/uBlock/etc. add it to their database?

You cannot stop that. You can get around it for a while by serving the script yourself and setting a CNAME record for your domain to point to us. That's why we recommend integrating Pirsch into your backend so that it can't be blocked: https://docs.pirsch.io/get-started/backend-integration/