Any thought of an "edited" comment like FB has?
When I edit it's either grammar or some such error. Otherwise I will sometimes use "ETA." But if it's a BIG difference I'll reply to my own post so that anyone who's already seen will see the difference. But sometimes people come back and pretty seriously change/add on to their post. And those of us who have seen or particularly replied to wind up dealing with a significantly different post. Just a thought.
One unfortunate flaw in the "already read" layout of a thread is that going in and changing a post already read or adding eta: and then add'l text to the same comment box might not be seen by your intended reader.
Seriously changed posts that alter the meaning of a comment you've responded to based on the original remarks doesn't always get seen either for the same reason I'm observing above. Once collapsed, I might not even realize my own comment is now out of context.
But if I do realize it the only way to address it is by adding another, new comment or asking for my comment to be deleted. Or, if I catch it during the 2 hour window of edit function now, rewriting it....which is a real pita.