I'd like to use the video and audio elements with the current markup (XHTML1 Strict), I wonder if that is possible and if is there any implication by doing that?
If the browser supports them they could be used, although the document will not validate. All of your XHTML1 elements will work with the HTML5 doctype though, what is preventing you from updating it?
Does not work for me. I tried upgrading my page by just changing the doctype and the page layout was affected. Tested on FF3.6.8 and Chrome too. Both support HTML5.