One place I used to frequent solved this by disallowing editing of the original content but allowing the author to add a small annotation after the fact. Doesn't really fix the "correcting typos directly" issue but does allow for clarifications, etc., without the possibility of changing the original meaning that people may have RT/QT/etc.

(You could also extend this to allowing the annotation to be added to a run of text and shove it in the entities object for extra clarity / highlighting.)