(I have a feeling this will be in the pipeline, but here goes.)
A common feature in help authoring tools, e.g. Madcap Flare, is to be able to undock a pane and have it float free.
Obviously, this is particularly useful if you have dual monitors. For example you could have the outline pane filling one screen, and the editor another.
It would also be useful for single monitors. For example, I need to consult a city map as I write. It would be nice to have the research file in a separate window which I could ALT+TAB to in order to bring it up. I appreciate there’s probably some cunning technique using layouts that would do this, however, this would be more intuative.
Scrivener for Mac has it, or a version of it. You can put any document into a floating Quick Reference pane. It will probably look a bit different under Windows, but should be in the pipeline.
Both the Freeform Corkboard and Quick Reference panes were added in version 2.0 of Scrivener for Mac. While there isn’t exact version parity between the Mac and Windows versions, that does give you an idea of relative priority. That is, in general you should expect to see Mac 1.54 features appear in the Windows version before Mac 2.0 features, and Mac 2.0 features before Mac 2.4 features.