• UPDATE: Industry sources are telling The Wall Street Journal that an improved API will be announced today. At launch free apps will add reviews, lyrics and concert listings.
• Several of the latest rumors center around closer ties with or even purchase of music intelligence provider The EchoNest. Since that company helps power hundreds of apps, that would jive with other theories regarding the launch of a Spotify commercial API.
• In fact, Eliot Van Buskirk of Evolver.fm (a blog funded by The Echo Nest) is convinced that Spotify will announce a commercial API that "lets app developers for iOS, Android, and other platforms build – and sell – music apps that  draw on Spotify’s catalog of 15-million-plus songs.
• Peter Kafka at All ThingsD agrees, but admits he can't find anyone to confirm it including app developers who might logically be the "special guests" that Spotify promised today.
• A Spotify web player in conjunction with the API is Janko Roettgers of GigaOm's theory: "Taking Spotify everywhere wouldn’t be half as spectacular if all third-party developers could do was to trigger plays within the app, or direct people to splash pages that ask them to install it. No, the real holy grail would be to actually play Spotify music within third-party apps and sites, with no additional software downloads required."

But to make this a "big announcement" of "a new direction", I think there will more. I'm also expecting one or more of the following:

• An iPad App. Hardly a new direction, but overdue.
• Big partner announcements of major mobile or ISP providers offering Spotify as a bundled and or discounted service. Spotify has done this with Virgin in the UK.
• Spotify's own US download store. No more sending customers off to iTunes, etc.
• Ticketing and or other "buy" options powered by new partners.  

A Wild Theory

None of the above is all that sexy, but collectively it might qualify as "big".  Here's a wild theory, but not illogical theory would make major headlines:

In an interview by Eamonn Forde for Music Ally, Jason Herskowitz of the "anti-iTunes" music player Tomahawk theorizes that "Facebook acquires Spotify in an all-stock deal that makes everyone investing in Spotify rich with Facebook stock. And Facebook doesn’t have to pay cash to get the service; they just have to pay for licences." Now, that would classify as "BIG". 

Tired of all this guessing and ready to laugh?  Stuart Dredge offers: Top 10 Things Spotify Might Announce at its ‘New Direction’ Event.