Matt M.: As you say “Don’t bother making Eclipse in a browser.” Having praised the idea of Ning and other “make coding easier,” those technologies have a poor history of panning out beyond the initial examples. The phrase “code generation” doesn’t bring up happy thoughts. That said, current “code generation” applications might be good enough to solve people’s problems, meaning they wouldn’t need to pay for a programmer to write an applications. For example, many companies run their financials in Excel spreadsheets rather than buying an ERP or other financial-focused app. That could be an analog for the success that “web IDE” tools could have.

All of the features you mention for Writely are already available as Eclipse plugins. With MyEclipse, I have a design/source page that lets me see changes as they happen, and drag elements of the page.

Now, could you build an IDE out of Firefox plugins- yes. But why?

What the web is good for: things like ViewCVS, Trac, SourceForge, etc. that let you browse source code repositories. Those things are moving in a web 2.0 direction.

You have various page creators for things like HTML- but that’s hardly coding. I also think you’ll see things more like the Ajax Scaffold Generator for Rails. These are things that let people build simple applications, or templated applications. Don’t bother making Eclipse in a browser.