I'm playing with this in CodeMirror (browser based code editor) which talks to a local node.js server, and I think it looks really good, as long as you have low

I'm playing with this in CodeMirror (browser based code editor) which talks to a local node.js server, and I think it looks really good, as long as you have lower and upper limits as you suggest. Biggest concern is stuff like the undo history. I think it just needs a "formatting" button or even background process when you leave it idle for a bit. Might be better to run on the browser but haven't bothered trying yet.