The approach to web service-based metadata deliveries is based on URLs that are set at the discretion of the company who publishes the web service to its business partners.
While it can be assumed that many URLs follow a common syntax, there is no compulsion to use this approach. Similarly it is not compulsory that all URLs from one company follow a common syntax.
All the Metadata Provider and Release Contributor need to do, is to agree the URLs for the subscribe and unsubscribe calls as well as the metadata delivery calls.
Wherever this standard mentions only the HTTP protocol, it is to be understood that HTTPS communications are also allowed.