I can only recommend difftastic[1], which is a language aware diff. Independent of linter that shows the logical diff, not an assortment of characters or lines that changed.
I think the use case would be limited to a handful of users (slight hyperbole).
The average user is content enough with using plain PowerPoint and won’t bother with Markdown. People using Markdown are more on the “you’re doing it wrong, put the basics on the slide” side.
The people that make nice backgrounds for their talk, sometimes with a word or two, won’t get there with a text based tool either.
People that use LaTeX, markdown or some other text to slides tool are few and far between.