Ensuring room history migrates to new servers when room membership/ownership does
History needs to be pro-actively copied to new/other servers so that the server on which a room was originally created (which for very many rooms is matrix.org) does not become the default or only source and a single point of failure for later history viewing. We need to think about this and define some useful rules, policies, admin tools, configuration options, etc.
In addition to room history, there are likely other matrix data and metadata that presently stick to the origin server by default. The same principle and similar mechanisms should apply to these too.
see: @Strypey raised this in Open Tech Will Save Us room, #otwsu:matrix.org on 2020-05-14: https://matrix.to/#/!AnacGSwlCZcUuAfcEU:matrix.org/$6IqpMYUGNPwDUV71Z58sX5cVsDa3RpfUQNnOzTO9GqQ see: https://github.com/vector-im/riot-web/issues/13680