Could someone tell me if this is possible and/or give me some tips, drawbacks et cetera.
This would certainly be possible by creating your own AJAX Behavior extending AbstractDefaultAjaxBehavior that "listens" on the user's clicks via javascript and sends any information you calculated within the javascript to the server, where you can react to it in the Behavior's respond() method. A tutorial on how to create your own AJAX Behavior can be found here.
The code would look something like this then:
MyPanel panel = new MyPanel("panel");
panel.add(new MyAjaxBehavior());
However, if all you want is drag and drop you might find existing solutions like Sven Meiers wicket-dnd.