Yah absolutely. A lot of the problems in #1 and #2 are already solved, with technologies like Bittorrent as you mentioned, although doing the work to make it work isn't trivial. #3 can potentially be complex. So at present I'm imagining that someone will need to "pin" on some machine under their control all the data that operates a given community, in order for it to be guaranteed that all that data is available. Someone has to guarantee the storage in order for it to be guaranteed that the appropriate data won't be deleted, and I think it's better to just be explicit with the requirement and let people decide how to configure their software. Then the issue is just that the technology works well enough that that data can be found quickly if it's needed, and cached on other servers well enough that you can run that "pin" on your own home internet or on like a $20/mo Digital Ocean account, as long as you have the disk space and a machine that can be available almost all the time.

That sounds simple, but there are weird little things to worry about -- e.g. what if a stored-in-the-shared-store community is abandoned, and part of it passes out of the shared memory of the system, but not all of it? At what point can someone else create a new community to replace it? What happens to little pieces of shared content that still do exist within the system when that happens? What if at some point the old community reappears? I feel like that can be dealt with reasonably well, but it's clear that there are questions like that that are uncharted territory which always has some surprises.