As an overall feedback and from what I have learned in experimenting several Cloud IDEs, the key thing of their possible success is really in the UI and in the user experience. And personally, I will definitely use one of them to build my web application in the Cloud if they do respect my current developer experience by bringing at least the concept of an IDE that can run in a single browser tab. And the reason is fairly simple, It is really costly in terms of memory to have many browser tab instances opened at the same time ( Youtube, Twitter....) and as stated by Steve Krug, the key thing to usability is this : Don't make me think.
You can see now what is going on when a file is opened with my concept of views and with my console (Config Button : show Logs=true). And any error during this operation is catched to launch the problems view so that my system can fall gracefully. Clicking on the views button at the very bottom of the page or Shift + V will show you all my registered views. And maybe, an outliner could be the next?