a la carte add-on ? [...]

Desirable but unfortunately not that easy to implement. Many features affect other files, templates or database tables.

If you for example want to port the AJAX preview from version 2.0 to 1.7 you need the JavaScript functions to show/hide the preview bubble, JavaScript functions for the AJAX request, a PHP script which fetches the message data from the database and parses the message, HTML and CSS for the preview bubble.

But I try to make as many as possible adjustable in the forum settings.

Alex