(UPDATED) Twitter now allows SoundCloud's HTML5 widget to be played inside of tweets containing a SoundCloud URL. This means that Twitter users can play SoundCloud tracks right inside of a tweet, allowing anyone to follow SoundCloud profiles directly within the new expanded Tweet.
UPDATE: According to SoundCloud, it is a "soft rollout" by Twitter and that it will be available to all users shortly
Twitter has been rolling out more of these interactive experiences (expanded tweets) as of late among a diverse and growing group of new partners like the The Wall Street Journal, Breaking News, TIME, and of course SoundCloud. These experiences deliver rich content inside Tweets containing a link to those partner websites (you’ve probably already expanded Tweets before to play videos from YouTube or view photos from Instagram).
Other expanded tweet partners include Lifetime, TMZ, WWE, Daily Motion, Lytro, BuzzFeed, MSNBC, The New York Times, The San Francisco Chronicle and der Spiegel Online.
With this new addition of expanded tweets among a wide pool of partners, Twitter is positioning itself to be that much more of an alternative to blogs and even destination websites by delivering full content experiences directly into their users' feeds.