Not a huge surprise, but good for her.
I suspect it was a career move.
She could have come out at any time, it's a not so well guarded secret in the industry for a very long time. It would have been more impressive if she came out during the height of her fame, post Juno.
But her last film, The East, bombed. More to point, she got critically panned in it. Her one "gimme" film, post Oscar nomination, to prove her box office chops, Whip It, failed. She had a non memorable part in Inception. There was that anti establishment super hero film, Super, where she tried to show herself as sexually aggressive that didn't make any money. That she's associated with the X men franchise, this was her last shot while her name would buzz once more to try to get some momentum going.
It's not her fault she looks like shes 16, and probably will most of her life. But it's limiting on the parts she can get. She simply doesn't look old enough to hold a film's female lead category for most adult oriented films.
Juno was in 2007, she's a couple of steps away from having to do television full time.
Maybe the saddest part is she looks just a few shades too old to play Ellie in The Last Of Us, the video game that will be turned into a film and a decent chance to be a hit or maybe a franchise, even though they stole her likeness without paying her.
What no one seems to mention when someone comes out, is the fallout. When Zachary Quinto came out, it outed Hayden Pantierre as a beard, which exposed Milo Ventimiglia and Scotty McKnight, which in turn, shone some light onto Mark Sanchez.
Might be great for Ellen Page, but she sort of left Alexander Skarsgard, who needs his leading man appeal with women to stay established, out hanging in the wind.