HTML5 has been around for several years now, but it's finally approaching the point where the standards are all agreed and finalised.. some 3 years on from when web developers and designers were given the all-clear to start using HTML5 on their websites and web-apps.
Although we shouldn't expect HTML5 to be completely finalised until the second quarter of 2014, HTML5 has become first-hand for many developers who already take full advantage of the new specification. If the HTMLWG (HTML Working Group) meets its set deadline of 2014, it will mark the first official update of the HTML specification since HTML 4.01 was released back in 1999.
But the question has started to surface, what comes next? The W3C have started collecting ideas under the HTML/next specification which is managed by the HTMLWG.
It was proposed that the HTML5 specification would become a 'living standard' with no definable versions, thus development would be on an on-going basis. However, potentially one day we will see a specification of HTML6 surface, though for now W3C have a shut-door until HTML5 is completely finalised.
Modular API Specification
The advantage of HTML5 is the way the specification is broken down into different APIs. This modular development process means that development can move at a varying pace and new technologies and consequent APIs that may depend on others, can be finalised individually, without needing to wait for other aspects of the specification to be verified.
This is a huge factor to take into consideration when addressing what comes after HTML5; it not only means that the development can be separated into key APIs but that the development of each is vastly accelerating, and the pace at which compliant browsers are implementing the new features and various aspects of the specification is also increasing (although, we could say the opposite on the topic of handling responsive images in HTML5).
I personally believe that HTML5 is a wonderful specification with a huge collection of APIs that developers still aren't properly aware of their existence. I think the next major step upon HTML5 being completed and finalised, is for developers to get a more thorough understanding of what the HTML5 specification actually provides - it's not just some new semantic markup, it's a whole catalogue of fantastic APIs that really lets you take full control of the browser and device a visitor is accessing your website on.