>Think about some sort of publish/subscribe system, in which a web-page creator can regularly hit a publish command that makes it available for archiving, and various web archives can subscribe to receive updates
This seems like something we could (should?) have right now. Maybe IA should write a Wordpress plugin, if they haven't?
I was vaguely thinking more of publishing and updating directly to IA through some kind of API, (rather than having them scrape everything - that may actually exist, I don't know), something you could even add as a button to a text editor. But that is pretty close.
I think you just reinvented https://pingomatic.com/