as javascript becomes more popular as a language for implementing standalone apps (see various gadget/widget platforms for example) i find myself occasionally working with javascript files in visual studio. visual assist doesn't do much for javascript development -- but i wish it did! just the smart autocomplete would be so useful.
i suppose that the visual assist implementations for each language are quite complicated, but sometimes i wish i could just describe a simple grammar for a language, and give it to visual assist so it could then powerfully parse those files, as it does with visual C++ and the like. sure, it might not be as powerful as the custom implementations for C++ and the like, but visual assist could still add a lot of its most basic features to development.
We have no current plans to try and add additional languages. Have you looked into other editors, perhaps Eclipse? I have heard of it, but never used it, so I don't know how suitable it would be for JavaScript.