It could be done without having to clone all data though. Reddit is hosted by AWS and their data is distributed on multiple servers, so replace AWS by a bunch of people like you and me providing disk space for the data and tada, you can decentralized the database and just give people access to interacting with it directly (through code) or via various front-ends that people would create. […]

If I understand you correctly, there is an open issue for Lemmy for an, I think, similar idea of co-hosting communities.