The four hottest topics in the WHATWG Issues List are:
- Finding a suitable common codec for the
- The accessibility of tabular data.
- Web Forms 2.
- Using markup from namespaces other than HTML in text/html.
The video codec issue is being actively worked on, but we're not close to a good solution yet (it's mostly an economic and political issue, not a technical one, which is why we don't have any transparency on this issue, sadly). I recently responded to most of the table-related feedback. Web Forms 2 work is waiting for a decision from the W3C's forms task force on whether WF2 will be integrated as-is into HTML5 or whether it will be changed before being merged. The namespace issue is the one I'm working on now.
The first thing I have to do is work out what the problem is! There has been a lot of discussion, but not much of it is focussed on a problem, most of it is focussed on possible solutions. One can't evaluate a solution without knowing what it's trying to solve, though. To this end, I have created a wiki page where I will note down any problem descriptions I can find as I read all 367 of the e-mails in this folder.
Feel free to help! If you want to coordinate, I'm Hixie in #whatwg on Freenode IRC.