Webhooks would be much closer to a sane solution to this use case. Why would you spam a web server asking repeatedly wether something has happened or not, instead of just providing him with an adress so that he can simply let you know in due time ?

It's not spamming any more than me opening their website myself in a browser, loading their entire webpage, looking "Is part 3 posted yet", and doing that every day until part 3 is posted.

Except this idea is automated, and wouldn't need to load the entire website.

Because then you have to maintain a publicly accessible server, and he has to maintain a database of everyone who has clicked the button. It wouldn't be "spamming", just loading a tiny endpoint once a day (or less!) is a trivial amount of traffic.

Doing it your way would be completely unworkable.