My impression is that the lack of knowledge of what/why is kinda the point: it's the server's job to make the intent clear (via hypermedia), and it's the client

My impression is that the lack of knowledge of what/why is kinda the point: it's the server's job to make the intent clear (via hypermedia), and it's the client's job to faithfully represent that intent to the user. The use-case is therefore related to that of the "semantic web": provide as much expressivity for that intent as possible, and make it as easy as possible for the client to faithfully convey it.