Revit models can be dragged and dropped to an open Docs window. This is fine for quickly looking at files - especially if you do not have the appropriate revit version available.
In order to make them cloud workshared, you need to remove them, open them inside revit, initiate collaboration, find your project again (which may still be open in your browser), go to the sub-folder you just removed the file from and ok it.
The idea is to allow to initiate any revit file from within the web interface. Any model older than or of the hidden version of the cloud project would be immeadiately updated to that version, newer models would not be altered. The logged in user needs to have the appropriate licences but other than that, I see no reason why this could not be implemented.