There are proposals in HTML5 to support a scoped css style attribute:

http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#attr-
style-scoped

This restricts applicability of a <style> tag to the region of the html where 
the <style> occurs.

Even more complex are proposals to scope style tags dynamically using web 
components (template, decorator, and element tags) with locally-defined 
<style>s and the ability to import by <link>.  See:

https://dvcs.w3.org/hg/webcomponents/raw-file/tip/explainer/index.html

Right now there is no browser support for these, but we'll need to have at 
least basic blacklisting / treatment for them in several of our filters, and 
preferably transition to supporting / using these features as they become 
standardized and have stable browser support.