Could you have possibly missed the news on Bespin, a project from Mozilla Labs? Don't see how. But read up if you haven't.
Bunch of rambling thoughts here:
Also check out Sun's Lively Kernel. In particular, make sure you click on the "Development Tools" link (blue globe/basketball thing) after you "Enter the Lively Kernel" to see their take on Smalltalk-like browsers for JS.
Bespin works it's magic with HTML Canvas, Lively Kernel uses SVG. Interesting, because these are two completely different low-level programming models, though perhaps we'll end up seeing widget toolkits built with both.
Implementing text editors with HTML Canvas and SVG leads you into the Uncanny Valley, as such low-level things as clipboard operations, cursor movement, etc all have to be implemented with user-land code. Doesn't sound like a great proposition, it's at least a crap-load of work to get all the expected text editing behaviors implemented.
But you know what, I think Uncanny Valley may not really apply to text editors. I use a large number of text editors in my day-to-day computer usage, and almost none of them are using any kind of a common "text editor component". Eclipse, TextMate, Notes, vi, etc. You just have to get used to them. There are certainly programs I use that DO use a "system-level" common text editor - in my case, the one Mac OS X provides. Forms within Safari, Twitterific, other apps presenting text areas, etc, all use the baked in text editor control, which is nice, because I get the same kind of spell checking, cursor movement, etc. I think extending the usage out to "code" editing (eg, syntax highlighting) just isn't going to work though. Or let's say it hasn't happened yet.
Although most of the focus on Bespin is on the browser bits, the impacts/opportunities for server bits isn't lost on some people. In fact, this may well be a more interesting piece; if you imagine an interesting set of back-end "IDE services" being defined for Bespin, why couldn't desktop editors also take advantage of them?
May you live in exciting times.