You're basing a lot of this off of current implementations of these websites. Which one of these could not be done (at least a large portion of it) in HTML5? Ea

You're basing a lot of this off of current implementations of these websites. Which one of these could not be done (at least a large portion of it) in HTML5? Each of these seems like there is HTML5 functionality to enable most of the functions and features of these websites.