As of rest-server v0.10.0, the “feature” to have sub-repositories was removed. As requested in the release notes, I’m making a post on the forums :).
My use-case is to easier support multiple repositories. I’ve build a plugin for DirectAdmin to integrate with Restic. Each server has it’s own HTTP user, and there is an option to have a repository for each user on that server - instead of the default, a repository per server.
I build this option a while ago, because some servers had thousands of users - resulting in even more snapshots (as we were saving ~60 days and a snapshot per user, per day). This brought down the performance so much, that I decided to add the option to automatically generate a repository for each user using the - now removed - “feature”.