This is Alastair Cockburn's original definition of a User Story from the XP days. The User Story is a deliberately-lightweight format of capturing a user need. As Future work is an option then there's no guarantee that this work will ever get prioritised. Rather, it's an option to defer detailed analysis of work until the point of most responsibility. That is, when it's prioritised for maximum value. Performing detailed analysis on a user story prior to this point is costly, because it may not be the next thing to do (in a sense, the option has been exercised too early) and can incur cost through rework.
The user story is a vacation photo - containing enough information to recall the context.
Through structured conversation, the user story can be discovered. Example Mapping for discovering unknown unknowns is one technique that can be applied to perform exploration of a user need.
Note that Metrics are a tool for a conversation and not the primary purpose
tools for a conversation
Environments that practice Agile in Name Only often decompose fixed notions of a thing to built into smaller 'user stories', that may not actually be user stories as originally intended - ie A User Story is a placeholder for a conversation .
A User Story is a placeholder for a conversation
A User Story is a placeholder for a conversation