I just tried to do this on another forum, and I was quite surprised when it didn't work
When you add quotes to multi-quote on 1.3, it would be a good idea if the 'Insert Quotes' button also appeared when editing a post, as it would allow users to add their quotes to their post without making another post.
I certainly agree with your suggestion. I've written a posting concerning the different worksflows when it comes to use multi-quote and the inability to add multi-quotes when editing a post is part of that indeed.
Again, I believe that a product like Burning Board works considerably better (and see also here) compared to XF when it comes to the use of multi-quote. And yes also in this case indeed, because when you use Burning Board it is very easy to insert your multi-quotes when editing a posting. In Xenforo it is simply impossible, making the whole system less useful.