Module that allows to compare, edit and/or merge revisions
I doubt there is an out of the box solution. But maybe you can Views of Pending revision items per content item using Views and if needed the Revisioning module and maybe Rules. Eg, somehow you want to list stuff with pending changes and Revisioning+Rules seems to be able to do that:


  Rules: when Triggers won't do, use the event-condition-action paradigm
  of Rules. More complicated to set up than Trigger, but very powerful.
  Revisioning adds its own events and conditions to Rules, for example
  "content is about to be published" and "content has pending
  revisions".


Then for the view itself you could try to link to a 2nd page that uses the Diff Different module to make the UI per field item you are talking about to move field data around.

I don't see any out of the box solution and you need to build a Workflow of pages/forms/views etc. I'm just trying to help by listing some tools to help achieve that.