In the case of most films, with most writers and most directors, this wouldn't necessarily be such a big deal – but here we're talking about the second Avengers picture as plotted out and to be directed by Joss Whedon.
In a new interview with EW, word breaks that Whedon has:
submitted an outline for the 2015 sequel The Avengers.
Glad to see we're not the only ones who leave out the odd little word here and.
One implication of the Avengers sequel getting an outline is that it suggests the whole of Marvel's movie universe phase 2 has some sort of shape now. Iron Man 3 promises to be rather untangled from the bigger picture, and neither that movie nor Thor 2 will feature an appearance from Nick Fury. He will be back for the Captain America sequel, however, alongside some other SHIELD types, so don't expect this next wave to be just a series of standalones. Not entirely.
Next up for Whedon is filming his SHIELD pilot. EW note that:
If ABC he picks up the series, Whedon will remain involved as exec producer, and frequent collaborators Jed Whedon, Maurissa Tancharoen and Jeffrey Bell will serve as lead showrunners.
Which I think is a slight modification of the previous assumption? Call it a clarification at the very least.
You likely want to read the whole thing – it's essentially Whedon's reflection on how well 2012 went.