I would like to be using visual studio to edit certain source files which are not natively supported. Say for example my own in-development script language, or the people which use Lua and other script languages. What I would like is at least the same support for custom highlighting as the editor EditPlus.
if instead you are looking for full blown support for new languages then the answer is going to have to be no, at least for now. we already have a lot of work simply keeping up with several IDE's and all of the quirks of C++, C# and VB.
And a support for hlsl files (gpu shaders language)? their complexity increase very quickly and the advantage of visual assist would be great for this language ( c++ with more built in type and some new call parameter semantics)