Since this had been a "future" development discussion a while back (re possible use of HTML5 in x2go) I thought I'd pass this on.
Just stumbled on this announcement of noVNC (LGPL3) and saw they now implement HTML 5 (websockets and canvas)
http://kanaka.github.com/noVNC/
their source is on Github
https://github.com/kanaka/noVNC
Brian