A couple I’ve thought of:

- Testing - when you’re developing a client/feature and you want a temporary relay for ephemeral data.

- Private chats - setup a relay, invite participants. One participant is a “broadcast” bot. Everyone DMs the broadcast bot, which broadcasts incoming DMs back out to everyone as DMs. The ephemeral relay would have the metadata, but all message content would be end-to-end encrypted, viewable only to members.

- Gaming - use a temporary relay for game state. May also include player comments.

But I’m more interested in what other people might use such a service for.