I assume them is a reference to state level actor? At least to me it is not immediately obvious and I think I misread it the first time.

Add to that a way to authorise people to decrypt your stuff (and, ideally, ways to revoke those rights), and you get the the whole thing.

But IIReadC you wanted to cache media on peers devices to allow them to see/listen to it.

That cannot work unless you trust your friends completely (or keep your friends under constant surveillance, and hardly even then) as once they see it on their screen they can photograph or record your media, if necessary using an external device (e.g. a camera) and store it or share it.

Also, once your friends has access to it that makes your friends a target for bad actors that might want to trick or coerce your friends into sharing.

This is just another form of digital restrictions management (aka DRM). I think you'll find that most of the engineers that are opposed in principle to the gov-tech surveillance complex are also opposed in principle to DRM.

It is at least possible to build an open-source distributed social networking application that gives you most of the features you described, and in particular, will make it impractical to vacuum up whole social network graphs.

But at some point, ordinary netizens are going to have to learn some basic information theory. Just as commando clubbing is going to lead to some paparazzi getting vagina pics, nude selfies are going to get out beyond your ability to control.