I've been wracking my brain trying to decide what I want to show at the upcoming conference, and decided I should get the new editor in a semi-workable state. I started laying out the interface two days ago. To my surprise, the whole process went very fast and I discovered some cool design features along the way.
With the freedom and control I have with the new user interface system, I was able to make the side panel extend all the way to the top and bottom of the window client area. This gives you a little more vertical space to work with.
The object bar on the left also extends higher and goes all the way down the side, so there is room for more buttons now.
The toolbar only spans the width of the viewport area, and has only the most common buttons you will need.
Right now, I am showing all files in the project, not just game files. If it's a model or texture file the editor will generate a rendered thumbnail, but for other files it just retrieves the thumbnail image from Windows for that file type.
All in all I am very pleased with the design and pleasantly surprised how quickly I am able to implement editor features.