Useful survey. The distinction I would add to the selection criteria is what the memory is actually for, because two very different things get filed under the same word.
Recalling facts about the user is a retrieval problem, where stale entries are the main risk. Recalling what happened earlier in this task is a state problem, where ordering and supersession matter far more than similarity.
Systems that treat both with one vector store fail in a specific way: a preference the user changed three turns ago is still semantically similar to the current question, so it comes back alongside the correction with nothing in the embedding to say which one wins. Recency and explicit supersession metadata are what separate those, not a better embedder.