I'd love to see the ability to do at least simple variable substitution in the href of an <a> tag. specifically if I could get CLIENT_ID transmitted it would let me track sessions between the a cdn and regular site. One of the big gripes we're getting from publishers is they have no idea if AMP is generating more or longer sessions or if users are just swiping in the carousel to another pubs content.

I realize that some of the variables are real time so that would involve intercepting clicks and that bring it's own issues. However if we could just get the static stuff that would still be a huge win.