Will any js libraries be updating api's with html5 under the hood?

Question

So there is a lot of cool stuff in the html5/css3 specs which should be able to replace a lot of the stuff that have been traditionally done with javascript.

Does anyone know if any of the major js libraries (jquery, mootools, extjs, etc) or any newer js libraries are going to be implementing their libraries in such a way that an html5 implementation will be used; but defaults to existing implementation (html4/pre-CSS3/js) when older browsers (IE8/FF3.5 and earlier) are used for backwards compatibility?

Basically, I'm trying to find out if there is a trend in this direction; or if this is kind of a reset point where completely new libraries are being written as opposed to mashups.