I recently switched a bunch of friends from a project-oriented whatsapp chat to self-hosted mattermost, because I wanted permanent storage for messages and attachments, and threads, and did not want to pay slack in perpetuity.

I feel that this idea is now in jeopardy, if I understand the 10k message history is the limit correctly.

And there I thought I had a solution to slowly bring over project channels, family related things etc. that was as reliable as "my linux box will be reachable on the public internet" and I am willing to manage that it does.

Seems I was wrong, but I don't know which other software has better future proofing.