They only have to worry about moderation if they host anything. They can keep Apple clean of social networks while endorsing and supporting an open protocol or format for fetching/presentation into a thin client (something like ActivityPub/ActivityStreams, to pick an existing implementation that could make sense to adopt/adapt). I don't know, I think that'd be a very "Apple" thing to do with integrations into the rest of their client side ecosystem.

> They only have to worry about moderation if they host anything.

I don't think that is the case. At least many users, possibly even most users, would not understand the difference between Apple hosting a social network themselves and Apple promoting a thin client that views decentralized content. If you have an Apple Decentralized Social Networks app, and a parent sees their child viewing objectionable content through that app, a bulk of their ire is going to be directed at Apple; they will likely not even know the name of the entity actually hosting the content.

The "we're not actually hosting it so we're not responsible" argument, I don't think it's ever really worked. I don't think it would work in this case. See: torrent websites.

I think the benefit to Apple also goes down. They give up control, and for what gain?

The trite answer is a modal going something like "the content you're trying to access A) isn't available on your <AppName-Level subscription> or B) isn't in our walled garden of third party providers". I don't like how it sounds but I'm confident they could sell that.

Heck, integrate it into messenger and treat all content like emoji/stickers you must acquire from a controlled source to circulate.