TechCrunch reports that sites using Facebook's Instant Articles will not see a decline because the format has reduced heavy code and limits advertising for faster downloads. Facebook also did not mention improvements to Instant Article users.
This update is just one of many things Facebook does to increase the user experience on the News Feed. Facebook said they rated users' devices and network connections, displayed fewer videos and more status lines if the connection was slow. They also create cache for quick access on mobile, download them before clicking to reduce download time.
This change will appear on the News Feed in the next few months.