If you do what you describe, the site will load minus all of its imagery and scripts, since those will be linked from a CDN as http://img.whatever.com/ or whatever. Anything linked with a full URL, nomatter how deep in your codebase will surface at some point in the future and throw up a scary warning for your users.
And you get to find homes for those 3rd party scripts hosted on http only domains.
And in my case I'll probably get to rewrite a Google Maps integration because that will have taken the opportunity to deprecate something important.
There really is a ton of work to pull this off. For every site on the internet more than a few years old.
And again, for zero benefit whatsoever except to clear the scary warning that Google plans on introducing.