I was at a .NET user group meeting last week. Scott Hanselman showed off the current development build; guess what, it has the same support for HTML, JS, Jquery, and CSS editing that it has for MS languages.
I guess you can try it yourself (if you have a VM or a partition to spare). Steven Sinofsky says they're going to make Windows 8 Developer Preview ISOs (with and without development tools) available to everyone:
