Hhmm 
So they have that gist snippet there, what they’re suggesting is that people implement that outside the highlighter (in that case, it’s marked.js, I guess the same could be done with highlight.js).
Do you think Discourse could do that? Or, previous question, does this make sense in terms of architecture?
I guess the general idea is just to do some find-and-replace, remove the diff marks, send it to the syntax highlighter, and then work on it with some more find-and-replace afterwards. It sounds very awkward but the truth is that the snippet isn’t that complicated at all.