I give you ++ for the idea, but I'm not so sure of the proposed solutions. I'm not sure they're actually better than using the blockquote tag and a hand-typed attribution.

I applaud your approach of stating more than one reason for a change, for considering and listing what the change would include, and for coming up with a possible solution.

The solution I use now is generally to just use the node id tag for the node I'm quoting ([id://673567]) and to blockquote anything I feel I need to restate verbatim in order to address.

The advantages of what I currently do are:

1. it requires no PM changes
2. it connects the reply back to the node
3. I only want to quote as much as necessary anyway, so copying and pasting is better for that than quoting the whole node and deleting large sections of it.
4. it doesn't force the PM code to track a potentially very large separation of potentially deeply nested punctuation that might be used for many other reasons inside the quoted section for every node as it's posted (this is an advantage over your specified possible alternative, but not over every possible solution)

It has disadvantages, but I don't think they're that bad:

1. I might have to type the name of the monk to whom I'm replying if I'm afraid the thread structure and the node id tag aren't clear enough (that's a pretty big if)
2. it does take a little bit of manual interaction, but then so does trimming the quote rather than rudely making a one-line response to a 200-line quoted section