Eventually we would like to move away from the use of wikitext to preview diffs in Visual Editor. Instead, diffs could be displayed in a WYSIWYG style. Perhaps with color highlighting, perhaps with strikeouts and boldface, perhaps with inserted annotations that look like marks a human editor would use.
Parsoid generates HTML diffs internally. So it would be nice to prototype a HTML diff UI based on Parsoid DOM (HTML5) diffs in Parsoid. If this is successful, it could also be used by Visual Editor (perhaps visual editor would request the diff from Parsoid).
See also: T21859: Remove HTMLDiff