Since writing this post, the link has been pulled down by Microsoft. Users will have to wait for an official release to test out the new twitter integration.
Tom Warren tweeted not too long ago that the Twitter beta app leaked. Upon downloading it, it was noticed that the apps primary addition is integration with the People Hub allowing you to import your contacts to the hub. It will also be noted that posting updates via the Me tile, to twitter, now opens the Twitter Beta app as opposed to posting via the me tile itself like before.
There are no other noticeable changes. Unlike its Windows Phone 8 and 7 predecessors, 8.1 is particularly noted for stripping out the Hubs into individual apps to expedite updates to them. The downside of this approach is that these hubs now do not function on their own and require third party apps to plugin to them to function effectively.
Update: Folks over at WPCentral have also noted Photo Hub integration of the twitter app. We can confirm that you can now see all your Twitter photo uploads via the photo hub.