It would be useful if JavaFX provided a docking framework which allowed a user of an application to change the layout of panels within an application. I was recently involved in a demo of a swing application which didn't have this feature but another application written in Silverlight did, it was seen as a very useful addition to functionality.

I would imagine that any panel that could be docked would have a title bar. Depending on where the panel was docked the title bar could be displayed as per normal on the top of the panel(frame!) or on the side (possibly displayed title vertically).

Perhaps as a panel was being dragged its contents or outline could be displayed and some kind of gravity effect could be implemented as the panel reached a possible destination.

The capability to define that a drop is an addition or a swap might be useful. So for example if a panel was dropped on one location it would add itself to an existing list of panels there, however you could configure the destination and/or source to specify a swap should take place with whatever panel the source panel was dropped onto.

Lots to consider but I think a fundamental requirement for a modern RIA.