What's really needed here is a tooltip when I hover over a change, and the tooltip shows me the last user to edit the text where I'm hovering, the date they made the change, and their comments for the change. There could be more UI than that, but attribution of changes in multi-edit view is the key issue that needs to be fixed. I suppose that could be done in a more complicated way using the histogram chart that is being created here, but it seems like an unnecessary complication.
There are 10 bugs asking for edit attribution as a feature and it was a top rated user request. See bug T2639: [Epic] Add feature annotate/blame command, to indicate who last changed each line / word