Fair point @grayswandyr. The user friendliness is the most important factor. An additional concern however is maintenance: if you go with self hosted, someone has to ensure that the server is up to date, vulnerabilities are patched and databases backed up. This is a lot to ask of someone, and that energy could be served elsewhere. Haven’t used matrix/riot, but if all of those factors are covered, then that’s perfect.
I feel everlasting is a bit of a strong requirement though: communities and community preferences evolve and change. Trying to choose a communications platform based on the criteria that it be everlasting means you’re potentially constraining your future audience. I feel it should be good enough to solve community communications now with the knowledge that this might not solve communication problems in the future.