-1
I think it's a bad idea because when you quote a post you are quoting it for what it currently says, not for what it could say in the future. Say, for example, someone posts "I like the colour blue". I might quote that post and say "Why do you like the colour blue, red is so much better". Then they edit their original post to say "I like the colour red" and now my quote appears like nonsense, where before it was a masterpiece. Also, it would not be a simple thing to implement as morpha says.