The feature I miss most is expiring messages. Yes, it totally depends on correct end-user client implementations and honest participants, but it is crucial for many scenarios where a client is compromised after the fact (or, lets say, an over-ambitious border control...). https://github.com/vector-im/riot-web/issues/2497
Hopefully this will be coming relatively soon once https://github.com/matrix-org/matrix-doc/pull/1763 is implemented. It’s mainly been waiting for someone interested in sponsoring the feature (which hasn’t happened yet).
