What if on link hover, some javascript code notifies the server and the server pushes the page? When the user clicks the link the page will have already been downloaded. Would that not be possible and useful?
You are making a custom request to ask the server to push something to the browser.
Browser: POST /preload?url=/next-page Server: PUSH /next-page
Just cut out the middleman and make a regular request.
Browser: GET /next-page
Even better use browser preloading mechanisms so that the browser knows how to best prioritize them. In fact if you do it this way the browser can even start downloading subresources and prerendering the page.
Maybe just adding a rel=preload link tag dynamically would be better (do link tags work dynamically? I have no idea). Or just fetching with normal ajax and use a service worker.
[1]: http://instantclick.io/ "InstantClick"