Everything in HTML5 is still changing. Look at the <time> element, lots of people were using this and it was removed and changed to a <data> element which had everyone scratching their heads as to it's uselessness.

Link explaining <time>/<data> change:
http://html5doctor.com/time-and-data-element/

And I'l REALLY not looking forward to building large LOB applications in HTML5/JQuery. All it's going to do is increase costs.