I saw something similar on another forum, so I decided to do it (in my opinion) better.
The quick reply now has:
As you type, compatible tags will appear in a small list that you can navigate with your arrow keys (press tab to put the selection into the editor).
As you type your bbcode, the tags are highlighted in a different colour.
Need to quickly edit multiple headings at once? Now you can. By holding the ctrl (or cmd on osx) and clicking in the editor, you can create multiple cursors.
Here's an old video I made when I was still working on it.
It's bound to be a little buggy, and is missing a lot of the available bbcodes, but if you notice anything wrong, please let me know.
EDIT: Just moved the files required for the quick reply to our server, as opposed to the shitty cloudflare servers that make it take a long ass time to load and don't load at all on occasion.