I personally know people in the casting world in Hollywood. They are looking at actresses. They are not in a hurry to make a decision as they want to get the script right. I can confirm Anne Hathaway and Amy Adams are front runners. I heard Emma Stone is being looked at too. I have not heard about Emily Blunt. Maybe she's also being considered in the second tier (Hathaway and Adams are 1st tier).
I don't know where all these "Emily Blunt is Mary Poppins" rumors come from. Maybe her camp is leaking these rumors. If you look at recent Disney casting announcements, they announcement the project, have the script ready, then they'll find the cast.
If they had selected an actress, it would've announced along with Rob Marshall's involvement this week (see Reese Witherspoon's involvement with Tinkerbell).
PS. I heard Disney wants a famous name. A big name like Amy Adams or Anne Hathaway. I also can see an up and coming actress like Emily Blunt. I think Michelle Dockery is good but she's not a famous name.
Updated On: 9/15/15 at 11:25 PM