That suggests the entire Admin portal will be quite transformed (it should be anyway, as it depends on so many screen reloads to update stuff). 

I’m not sure how the public view of the sites it generates would be affected, but take a look at other dynamic sites that are using lots of js to create what the user ultimately sees. In particular, run a Google query and then look at the page source and consider how you might parse it to pick out the various screen elements. They used to spit out a very nicely structured HTML page. Now it’s a horrible mess because Google has bent over backwards to make the content generation as hard to scrape as possible. I don’t know if WP would do that, but some users might want to make it hard for bots to scrape their sites, so why not?