This is a very nice Shortcodes plugin!
I have e-mailed you and am posting here as well so others can see what I wrote.
General for everything: Custom CSS box with the CSS div tags included. To define additional CSS values.
Background colors, border values, text color, etc.
It seems a lot of CSS values can be repeated for many of the shortcodes.
Icons in general. Include browse for ones own icons. Or a web page to see additional icons.
What about including curved corners.
Browse for Box Icon.
A web site to where one can see the names of the icons.
Browse for open and close icon.
Background color or open and closed box. This and more can easily be defined in the CSS values. Open and close icons are more difficult to define through CSS.
Counting down to 0 and then something happens. Go to another page, show some material etc. It could also be a date. It can be pretty complex and very useful. As in I run a film club web site and people sign up for our screenings. It could be with a hidden count down and when it reached zero anyone who came to the page would automatically be redirected OR another option the signup for would be hidden and another message would come up saying signup for the next movie has closed.
Browse for unique divider. I know I have downloaded a few very cool dividers and it would be nice to browse to find it and use it.
Line Width: Also include px where it says By Default it's 100%.
Align: left, center, right.
Background image would be neat to have. Like in the old books.
Up or down in relation to line. Forgot the name of it.
Big Infobox with button:
All the features to adjust the button. Similar to what I mentioned above.
Add some additional features like pins etc.
I have looked through all the shortcodes and I am very impressed with your work!
Have a great weekend!
Let me know when you plan on making some updates I will then very likely add a video tutorial of your plugin to my web site.