Maybe the existing Arduino IDE just needs to be able to utilize 'plug-in' options such that one could utilize any existing text editor they wanted? If the Arduino IDE had the means for such optional expansion we might have the best of both worlds, a simple default for beginners (much as it is today) but easily expandable for more advance users. I'm certainly over my head here as far as whats possible or practical, but I agree that the simplicity of the Arduino IDE is one reason for it's popularity in my opinion.
Lefty