The message to the press said: "A small team has been working on a big idea".
The speculation in the news is A) An RSS Reader B) Instagram rolling out video
Neither of these are "Big ideas". It would be as if Facebook had a similar announcement for it's "Hashtag" rollout last week. Copying Twitter is not innovation or anything to get excited about, so "hashtags" were announced with little fanfare. Similarly, holding a big event to announce they are adding video, is that really a "Big" idea? Come on.
Probably something that drives revenues too. Adding video to Instagram wouldn't boost the stock much since nothing is monetized there yet. Stockholders want to see products that drive revenue, and my bet is this announcement is something that does.