@andrestaltz, do you remember BBS? the dialup kind running PC Board or Remote Access? If you were using it back then, there was a very popular solution for message boards and offline viewing/replying to threads called qwk files) and also Blue Wave files) which were compressed files carrying the messages and threads. It is basically what you're trying to build here and for me still the best UX ever. I miss Blue Wave reader a lot. Here are some screenshots of MultiMail which was similar to Blue Wave (I couldn't find screenshots for blue wave).

Anyhow, if the file format is easy enough to write and read, this could sidestep muxrpc and flume and be a new way to SSB with friends.