Even though none of the 4 major browsers of the moment have fully completed the implementation of CSS 2.0, the working draft of CSS 3.0 is already underway. From the looks of it, CSS3 may be designed to extend some things and replace others in the current spec of CSS (2.1).
More stylesheet languages?
But what if there were more stylesheet languages on the horizon? What if another group of companies decided to create their own stylesheet language standard to be "a better CSS than the W3C's CSS?". Or what about a number of derivative subsets of CSS to appeal to other applications, such as user interfaces or page descriptions (come to think of it, doesn't SVG use a subset of CSS already?)?
Just how many more stylesheet frameworks will be created then?