HTML5 form attribute for form associated elements

As I was reading through the differences doc I noticed that HTML5 is
making it possible to move form associated elements outside of the form
tag. This is a good step, I wonder though, why not go further and allow
all but the submit button to be associated with multiple forms? I have
many times needed more than one form on the page and if I could share a
couple of those elements between forms (especially the hidden elements),
that would be much simpler. Ideas?