Federation makes that a challenge, but I do think having some addition to the protocol that allows like-minded or similar communities to group together and share material would go a long way towards people's concerns on being on the "right" instance, and aid in cases where one instance disappears. Such grouping could be moderated and federated just like the instances are, so if one group only wants particular things shared or pulled they could control that too.
I have no idea what effect such a thing would have on the federated infrastructure.