Still, I think this raises an interesting question: is it more beneficial to choose exactly the right language for each project in isolation, or to adopt a "good enough" general purpose language that can be learned in more depth by the development team, and used together with comprehensive library support and a strong and familiar IDE?
Eclipse is a step in the right direction in terms of openness and universality. But the editing experience still sucks. And it's harder to extend and customize than it should be.
There may come a day when there's an IDE that a) has a great editing experience b) is fast, flexible, and universal, and c) offer not just crutches and marginal improvements, but radical, order-of-magnitude improvements to the way we interact with software. It's not today. But the linked research project actually has some promise.
Are you sure? I would expect that the process of physically typing in the changes you want to make takes only a fairly small amount of time, certainly much less than understanding the code that will be changed or designing the new part.
However, the typing is just mechanical grunt-work that tends to distract from other areas. If it can be automated with good refactoring tools and the like and so minimize the distraction to the developer's thought process then so much the better.
Emacs may have a shallower understanding of languages than an IDE, but the breadth of languages it understands is pretty amazing.