"I think xCode e.g. which I use every day could easily be made into 3 different programs. 1) Project management and configuration. One program where you define which pieces go into your project. How they are compiled, deployed etc. 2) An Editor component which does syntax highlighting, refactoring, code navigation etc. 3) A GUI designer."

We used to have that. The GUI designer being separate was never a good situation, considering how one would connect the IBOutlets and IBActions.