pim:storage in the profile should exist, according to the spec according to @csarven:

Clients can discover a storage by making an HTTP GET request on the target URL to retrieve an RDF representation [RDF11-CONCEPTS], whose encoded RDF graph contains a relation of type http://www.w3.org/ns/pim/space#storage. The object of the relation is the storage (pim:Storage).

@matthieubosquet believed this wasn't the case and was going to respond to the linked chat, but since @RubenVerborgh asked me to report it anyway, here we are :)