Twitter recently changed its prompt question from "What are you doing?" to the more open-ended "What’s happening?"—triggering  the sort of intense discussion and analysis that any small change to a cherished social media site provokes. What's the subtext of the new text?   

The new prompt clarifies the site's mission: Twitter was originally (and modestly) concieved to let people post "personal status updates," says Barb Dybwad at Mashable, but it has evolved into a broader discussion forum and an outlet for "citizen journalism." At very least, "what's happening?" makes the site more intuitive to new users.
"Twitter drops 'what are you doing'"

It signals a shift from "me" to "we": As Twitter has evolved, users tend to maintain "threads" rather than speak in "isolated tweets," says linguist David Crystal as quoted at ValleyWag. And while the old prompt "looks inward," the new one "looks outward."
"Twitter's new prompt: A linguist weighs in"

Let's hope "what's happening?" reduces oversharing:
Maybe the new prompt will diminish "the number of useless and pointless Tweets about people’s personal and private situations," says Bertrand at Erictric. Though I still "am not a fan of Twitter" this tweak might make the site less objectionable.
"Twitter changes default question"