In the Camunda modeler, you can only expand the subprocess, but not link it to a different model.
While I see this is the current behavior and there doesn’t seem to have anything changed since Sep’ 16, where @nikku said
There are no plans to at [a workspace] functionality right now.
I’d like to discuss an implementation of this (implemented like the element-templates (JSON): either in the central (user) camunda folder or in a .camunda/workspace folder anywhere in the current model’s directory structure). Should this be done here or in the issue tracker?
The goal of the discussion (if it would be accepted) is to add this function via pull-request.