Surely there's a step between self-hosting on your home computer and colocating a server you buy

Surely a $15 per year vm would be enough to receive a few thousands POSTs per day (https://tinykvm.com/), or if that's not enough, paying less than $5 per month for a VPS is still cheap

Surely transposing a binary hosted on vendor A to vendor B is as minuscule in involved labor as configuring a webhook

I'm not trying to diss on your own reader which is an awesome thing to do, I'm just sad that resorting to a fully proprietary architecture is an automatism when considering a protocol that can't be more open than RSS