I think there is a bit of misunderstanding from the links provided, and maybe its the way that they are written. So let me try and clarify. Please let me know if this helps:
If a user needs to be a "Collaborator" on a Revit model (that is, making changes to a Revit model with the need to sync the changes back with a Central file) then that user needs a subscription to Collaboration for Revit, whether its monthly, quarterly, or yearly. The most cost effective is a yearly subscription, because its $400 per person cheaper per year than the monthly/quarterly options.
If a user is a "Contributor" to a project, and do NOT need to sync changes back to a Revit Central file, then they can simply be an A360 Team Member. An A360 team member could be a non-Revit user, but could still contribute to the project by viewing the model in the A360 Project Hub. That person could also mark-up, comment, see properties, etc of the model and any/all of the published 2D sheet information, plus any other project documentation that has been posted to the Project Hub, such as Word files, XLS, PDF's, photos, specs, sketchup models....nearly anything can be viewed in the A360 Project without the need for plug-ins. A contributor could also download a Revit file, and open it locally in Revit, with the understanding that its a downloaded "copy" and changes cannot be sync'd back into the Central file. They could, in turn, upload that copy of the model back to A360 Team, but it is still a detached copy, and will simply be an uploaded RVT file that others on the team could view. I could see this example being true: A PM downloads a copy of the RVT file, makes some changes as a "what if" scenario, and then uploads that back to A360, where the rest of the team can review the proposed changes, and then make those changes as necessary to the C4R workshared model.
So a "contributor" has access to the project and all that is going into the project, but cannot actively work in a Revit Worksharing session with local files/central files.
Only a Collaboration for Revit user can workshare with local and central files.
The entire team that are either C4R licensed, or just A360 licensed, can view, search, and socially interact, on the A360 Project site.
Scott D Davis
Sr AEC Technical Specialist