What about like just readable fragments of materialized views that were encoded into the messages themselves. So that a sharp local context and a blurrier larger context could be reconstructed from any given message. Sort of like a Mipmap. And with maybe 10% of the messages in a thread you could reconstruct a fairly accurate representation of the whole thread, at least good enough to run a search on. Every client could serve as a relay that stored its own threads and a constellation of associated mipmaps, and, if some were missing messages, it would be obvious which other clients needed to be checked for the missing portions the next time they logged on. Old/archaic data could be warehoused by clients that chose to do so. No central servers at all, you just crawl client to client looking for the connections, and build your own graph based on what you're looking for.