Well it's not really about extending ActivityPub. It'd be about servers/instances declining to act on such content as it comes in.
Instance owners are free to do with their computers as they wish.
@volkris yes, I agree, this mechanism is orthogonal to ActivityPub because as it is the vocabulary doesn't really have any support for SPAM specifically.
It's still possible that automated, or admin/user intervention on SPAM marked content to be Flag/Block/Ignore on the actor/instance that sent it, but I think that over complicates things.
Yeah, I think it would be worthwhile to standardize a tag that could mark content as advertisement/commercial, assuming such a standard doesn't already exist.
I could imagine a bunch of people being upset by the proposal, though, seeing it as enabling spam, which I'd say is misguided as it would do more to empower users to deal with spam.
