This post has been updated to take into account a mail from Björn Höhrmann with a heads-up about missing elements in the XHTML 2.0 list of elements.
The future of (X)HTML appears to be searching its way between two conflicting visions:

The W3C and its XHTML 2.0 Working Drafts.
The WHATWG and its HTML 5 counter proposal

I have [...]