With the HTML5 spec' finally completed and standardized on Oct 28th 2014, it seems logical that work should begin on it's successor, the next iteration of HTML, or simply HTML.next!

HTML6 is somewhat of a reversion back to the earlier concept of XML namespaces in HTML4. You're probably all familiar with:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> - http://www.w3schools.com/tags/tag_DOCTYPE.asp.

HTML6 really plays on the idea of namespaces rather than "tags" for semantic markup. In concept it allows the freedom to define any tag you want as only it's namespace is reserved.

Example: <my_tag:body>, think of it as <[custom_tag]:[namespace (traditional HTML tag)]>

It's still incredibly early days and I'm sure, just like with HTML5, which spent a good few years in draft but was implemented anyway through countless vendor prefixes/polyfills in most A+ browsers. So shall HTML6 when it get's off the starting grid.

Some of benefits it brings are:

  • Improved browser sizing of imagery. On the fly-optimization for different devices - RWD rejoice!
  • More control over the video object, and other media types
  • Seamless camera incorporation.
  • Possibility of including certain JS libraries. Notably jQuery.
  • Hardened Authentication and Security.
  • Solidification of Microformats (such as RDFa, MicroData "Rich Snippets" - Google).

HTML6 - Further Reading

CSS4 - Further Reading