Never mind redux or something - I am solely asking about Immutable.JS, Ramda, etc.
If new versions of a data structure is created by structural sharing, that means that every new version needs to have a pointer to the previous version in order for it to be able to share anything. That again means that older versions of a structure cannot be garbage collected, meaning again, that in an app where you have state, this state will use a monotonically increasing amount of memory. If this is the case, then that data structure will at some point have used all available memory, if it keeps getting modified.
Am I missing something here? I can see that for many (most) use cases on the web (in a browser), this won't be a problem, as you are probably just changing a tiny part of the structure each time, and you will probably leave the page or reload it way before you use all memory, but for long running processes this should pose a problem. Right? Riiight?