According to Comic Book Movie on Jan. 29, recently the Russo brothers are being called back for "Captain America 3" and the previous writer and co-producers of "Thor: The Dark World" have been hired on for "Thor 3". Craig Kyle and Christopher Yost's roles will be that of writers and will be partaking in phase three of the Marvel Cinematic Universe.
“I am proud of Craig and have enjoyed working with him over these past years. His creative instincts have helped shape Thor and Thor: The Dark World at every level of the filmmaking process. The entire team at Marvel is very happy to continue collaborating with Craig as he continues as a screenwriter working with Christopher on the forthcoming chapter of Thor’s adventure".
It appears that with abrupt haste in which Marvel Studios is moving forward with such rapid pace. That being said, it does appear that the studio feels that these upcoming sequels may do well and thus the rapid movement of already taking on crew members to start development of phase three. Marvel Studios already has Edgar Wright's "Ant-Man" in the works as well as Joss Whedon's "Avengers 2" film which pretty much supports the mapping of the Marvel Cinematic Universe.