Since Google+ launched over the summer, Facebook has been adding oodles of new features and tweaks. (Have you looked at your newsfeed today?) But it's widely expected that Facebook will make a "massive," game-changing announcement on Thursday — something much bigger than the recent additions of Subscriptions, new photo-tagging rules, and even the revamped newsfeed. What might it be? Here, six theories:

1. A whole new way to consume media
Facebook may "unveil a media platform that will allow people to easily share their favorite music, television shows, and movies, effectively making the basic profile page a primary entertainment hub," says Ben Sisario in The New York Times. It's believed that Mark Zuckerberg and Co. have cut a deal with Spotify and Rhapsody, two popular cloud-based music services, along with a number of smaller media companies. The agreements would reportedly allow a user's profile page to display whatever media he or she is consuming via these services. "If it works the way it is supposed to, it would be the nirvana of interoperability," says consultant Ted Cohen, a digital music/media expert.

2. A whole new look
"Facebook plans to roll out a major redesign of user profiles" to go with the new media-sharing capabilities, says Ben Parr at Mashable. While details remain skimpy, it's rumored that profiles will be more "sticky," in an attempt to try and get users to remain on them for longer. The redesign might also be part of a "larger push into social ecommerce." Is a Facebook app store on the way?

3. Some new buttons
There's buzz that Facebook will unveil "new buttons on the wall that will begin introducing some granularity to the 'Like' concept," says Leena Rao at TechCrunch. These buttons will reportedly be "Read," "Listen," and "Watched" — allowing users to note on friends' walls what media they've consumed. It will also allow Facebook to gather a wealth of information about users that it can then share with advertisers, allowing for micro-targeted ads. Handy!

4. A movie rental service
"In another effort to make Facebook's website 'stickier,' Facebook may officially debut a movie rental service," says Sarah Jacobsson Purewal at PCWorld. The company has already offered a handful of movie titles from Warner Bros. and Miramax, but it might announce a much more comprehensive offering. With all of Netflix's issues of late, "it might be the time to really strike."

5. A retro photo-filter app
Instagram, the iPhone app that allows users to take snapshots, imbue them with retro colors and effects, and share them with friends, has been a big success, and it's rumored that Facebook wants a piece of the action, says Jacobsson Purewal. Reportedly, Facebook is considering launching its own photo-sharing app with retro filters that would be a mix of Instagram and Color, and, theoretically, overtake them both.

6. And... something for the iPad
"It's hard to believe, but the world's most popular social network still doesn't have an official iPad app," says Jacobsson Purewal. Maybe Facebook will finally announce its iPad app... or a secret endeavor called "Project Spartan." Spartan would reportedly let Facebook bypass Apple and all its rules with a "totally revamped mobile website," all in HTML5, that would allow users to easily use the social network through a tablet browser, rather than an official app.