Thanks for the answer. For instance, usually those containers are used as indexes in DBs, so they contain pointers to data, not the data itself. That is an scenario where the references shouldn't be invalidated.

Idk if it may be possible to introduce "semantic monitors". Say, a field within a class and an external container must be updated together. In practice the only time when I have needed to break the single ownership is for keeping internal data views. I know it is safe, but convincing Rust of that is painful.