I also support this idea, with the addition that I would prefer the code / web views to be one above the other, if an external keyboard is connected. That way one would see the website in full-width. Another option could be to view the website on an external screen connected, while having the code open on the internal screen (AirPlay screen feature). Cheers!

Another advantage over Firebug Lite would be the possibility to detect JavaScript syntax errors and exceptions and undefined values, as the console wouldn't have to run in JS itself. This would be a huge improvement. Here is an example on how this feature could be accomplished with the iOS 7+ framework JavaScriptCore: http://www.bignerdranch.com/blog/javascriptcore-example/