Please also consider the concept of categories.
http://wiki.slicer.org/slicerWiki/index.php/Documentation/4.1/Extensions/CatalogPolicies

Revisit this when working on the new extension description (s4ext) file for Slicer5.

The new infrastructure can support multiple applications, multiple releases per application, and a collection of extensions for each release
See https://github.com/girder/slicer_package_manager/blob/c307bd3bae54a7640222d17e768a47d33697db9d/README.rst

To support the idea of "channel", few possibility:

Each channel as an application

(1) each channel could be implemented as an "application" (in the terminology of the slicerpackagemanager project). We wouldn't have to change the backend to support this.

We could then have the official application named Slicer with the official extension and an other one named SlicerUnofficial. Then from the extension manager, a drop box would allow to select one or the other.

unofficial channel in user space

(2) the official channel would be a folder in regular collection. The unofficial channel would be in user public (or private) space. Since the server rest api already supports creating application in any collection, we could simply add new api endpoints to:

• list all collection having applications. these would be identified by a metadata
• create a top-level collection in a user space

Then, the user interface would list all channel (aka top-level collection with a matching application)

This is now tracked in https://github.com/girder/slicer_package_manager/issues/52