Currently, editors can subscribe directly to artists, labels, and series, and indirectly (via collections) to releases and events. Conceptually, a list of directly-subscribed entities is not that different from a collection, and as collections will be available for all entity types soon (
MBS-8004), it would make sense to use them instead of having a separate list-keeping implementation. To be a full replacement, this would require MBS-8003 so that subscriptions emails not only list the collections, but the individual entities within them. The "subscribe me to all artists I create" etc. preferences would need changing so that an editor could specify a collection to which the newly-created entities should be added.
This would resolve various requests for subscriptions to entity types that don't have them at present (MBS-6855, MBS-3951; not MBS-1228 though, because it seems it isn't actually about areas but about entities associated with areas). It would also resolve MBS-8267 because collections display tables with more information about their contained entities than just the name.
It would also mean that editors could have better organized subscriptions; e.g., separate collections for more or less important entities or for different genres.
Finally, it would remove duplicated functionality and code.