No HTML6 On the Horizon: Versioning for HTML Is Over
According to the working group, there will be no HTML version 6, or 5.1.4, or any versioning going forward. HTML will be looked at as a "living document" that will be updated on an ongoing basis.
New changes to the markup language will be annotated on a section-by-section basis. The standard is dynamic by nature, and the group has been working hard to finish the HTML5 specification by 2012.