It's almost what I was thinking about!

What I'm wishing for, is the possibility to edit one of the copies and let the changes be applied automatically to the other copies. 

Let's say you're creating a pop-up window that you want to be shown on multiple pages. After you have created it and copied it over to the pages you want, every kind of change done after that, would have to be manually applied to every copy. So it would be really great to have the possibility to turn a group or an object into a instance (global instance) that would refeer to their copies and automatically apply changes to their copies. 

You can do that by adding a button, or any other clickable elements that will automatically scroll to specific element on the page. Try adding any element at the top of your page (can even be invisible one) and add "go to object on page" interaction

You can already do that by changing the size and position of most elements into vw and %. By doing that, the content will resize to window's height and or width.