[GoldenRivet]

My own research into the subject has revealed speculation mostly... but with a sprinkling of encouraging fact

1. for some sort of legal reasoning the name was changed presumably from Masters of The Air to The Mighty Eighth at some point during pre-production

2. spielberg and hanks have gone into media blackout mode on the subject

3. according to IMDB pro the series status is "in production"

4. at some point in 2014 through 2015 several filming locations were selected in Georgia, USA and throughout the UK and Europe.

the most recent mention i can find which seems to have any basis in fact is an article from earlier this year... the reason i say it is based on fact? well...

On the news page from the Lafayette College in Easton Pennsylvania, where Donald Miller, who wrote Masters of the Air, is a professor. An article is printed on the University web site discussing an upcoming appearance by hanks to the university for an informal interview in their gymnasium which was to include Miller

so, as of the time that hanks was set to visit the College where Donald Miller is a vice president and Professor just 9 months ago the media page discussing Hanks' visit states:

HBO is currently developing a dramatic miniseries produced by Hanks and Steven Spielberg and based on Miller’s bestselling book, Masters of the Air: America’s Bomber Boys Who Fought the Air War against Nazi Germany (2007). The series will tell the engrossing personal stories and exploits of the men who flew with America’s famed Eighth Air Force over Nazi-­occupied Europe.

Miller is widely acclaimed for his books on World War II. He previously worked with Hanks and Spielberg as a historical consultant for the ten-part HBO series The Pacific (2010), which won eight Emmy Awards, including Outstanding Miniseries. He was also the on-camera historian, writer, and chief consultant for the series’ accompanying documentary.

The link to the university media page can be found here

additional research finds that the Hanks visit did in fact take place, he visited the campus, conducted the interview among the faculty, staff, and alumni with Mr Miller obviously in attendance where it can certainly be assumed beyond doubt that the mini-series was a topic of discussion

according to media released pertaining to Hanks' visit to the university, the visit did in fact take place and the story states;

Hanks and Miller have collaborated on several World War II-related projects, including an upcoming HBO miniseries based on Miller's bestselling book "Masters of the Air."

this information comes from lehighvalleylive.com, a news media outlet local to Easton, PA and a link to the article can be found here

finally, the Lafayette colleges Flickr account (here) posts an image of Hanks mid interview with the caption

Oscar-winning actor Tom Hanks visited campus Monday for an informal interview with President Alison Byerly and Donald Miller, John Henry MacCraken Professor of History. The next day he met with Miller’s history students and discussed his preparation for roles in movies such as Saving Private Ryan and his involvement in the upcoming HBO miniseries Masters of the Air based on Miller’s book. He later sat down for lunch with Byerly, Miller, and small group of students.

it is my supposition that if Hanks had visited the university and had given the impression during his campus interview at Lafayette College that the series was in limbo or had been cancelled or stalled in any way, there would have been little to discuss regarding the miniseries and there would be information to the effect of it's cancellation somewhere in internetland, and at this time, production is still a go