I would like to see the ability to have a split designer window , like Visual Studio, Notepad++, or Eclipse already have. Having two tabs up side-by-side would be a great help when comparing two windows or even copying content from one to the next.
Along with that, I think it would be nice to have some of the scripts show up in tabs so that I could view them full screen and have them up next to other scripts or even next to windows that are using them. I understand keeping the event handler scripts in a separate pop-up, but it would be nice to see my gateway scripts and my script modules as full tabs in the designer.