How to Display popup block when user scrolls down to the bottom of node
You could do It without modules using some CSS and javascript.

You can create the block with the content you want to show, keep it hidden by CSS and, once the user scrolls down enough, trigger a js event that toggles the blok class to a visible one.

Here You can find how to trigger an event when scrolling to a certain point:

https://stackoverflow.com/questions/21561480/trigger-event-when-user-scroll-to-specific-element-with-jquery

Using the example code, you could use something like:

$(window).scroll(function() {
   var hT = $('#scroll-to').offset().top,
       hH = $('#scroll-to').outerHeight(),
       wH = $(window).height(),
       wS = $(this).scrollTop();
   if (wS &gt; (hT+hH-wH)){
       $('#yourblock').toggleClass('visible');
   }
});