How are you solving the diff problem? Word based diffs tend to be jumpy and hard to follow. On the other hand line based diffs do not work well for text (prose).
I'm doing 'fragment diffs' (doesn't really have a name) - but basically, all the text is displayed as you would read it (sentences and paragraphs), with diffs displayed inline and colored. Added content in green, removed content in red - doesn't matter if it's characters/words/sentences/paragraphs - it all works.
Screenshot is not the best, but something like this:
Code is easy enough to read in a unified diff because lines are usually short (unless java). Prose flows a lot more fluidly, and there is no formal grammar for human language. I have had the displeasure of having to read "redlines" (prose with inline diffs marked in red strikeout) and I find them completely impenetrable.
If you're using markup then encouraging the period-double-space could be a harmless way of easily breaking the document up by sentences