Hello,
Having some fun with the scribunto possibilities, I also found some drawbacks in the UX. Having to scroll to switching between the code panel and the debug panel is prohibitive. Making a better web IDE is possible, take a look at [1] for example: at one glance you have the documentation (exercises specifications in the case of the previous site), the code doing the fine job, the code testing it, the debug/result console.
Now one may prefer to use it's favorite editor/IDE anyway, in which case one may wonder how to proceed to get and install scribunto librairies in order to test the code on the local box. That should be documented somewhere, as well as how to make a git/mediawiki bridge to ease the whole process. If such a documentation already exists, please point me there.
Ok, that was my "thought of the day". :P