Cool? Yes. But is there anything besides "cool"? Probably not. Seriously, what's the reason to build web ide? The reason for some sort of web word process, i.e. google docs, is clear. But IDE? Thinking about pros of this tool i can only pick three, first one is access from anywhere, which is not that important since most developers can take their laptops and all the tools they need, when they need to. Second one is editing source files simultaneously which is rarely required for programming work. And the third one is an ability to deploy to different servers and architectures, testing you app on lots of different hardware and OSes, which is pretty cool, but it's hardly an ide job. But having only this three cons (name others?) is not a very valuable argument.. Now, even i don't see the point in this things, to get something useful out of it, it should provide two features, first one is extensions language which would be capable of expanding the functionality of ide, only not plugin-like shit, but more as elisp for emacs. And second one is an ability to edit files on some user provided machine, think or slime & swank.