I can see how this might work, and how it could be useful.
However, there is a significant challenge in designing this, both in the abstract, and in the technical implementation.
How exactly should it work? For instance, if three people have edited the same paragraph over the last 18 months since article creation, what do you show, and how? Do you go down to individual sentences, or even words? What about content which was removed?
Also: what is it about
the current diff viewer functionality that you find inadequate? For me,
the way it displays revision information is useful already.
For the avoidance of doubt, I'm not saying your proposal is a bad idea, but that there is already some quite powerful related functionality.