In 4.4, we're going to be enabling support for Lazy Loading. This will cause pages to load more smoothly as assets further down the page won't load until they come into view. Should help to improve loading times site-wide. Furthermore, we'll be improving non-image attachments to posts, providing more details about the downloads (such as download count, type of download, etc.). The letter avatars, for those who haven't uploaded an avatar yet, will be swapped to an SVG from the current image. This should be faster to render as well, since avatars are called in a lot of areas of the site.
Other notable improvements:
Duplicate Clubs query removed from activity streams. Notifications and follower management will see an improvement (Hope to have more on this in a bit, this is provided from the CMS) Member search speed should be a bit better. PHP performance improvements, to help with site speed.
Hopefully more to come soon, stay tuned!