During the press junket for Avengers: Age of Ultron, director Joss Whedon was asked about Agent Coulson's involvement in the movie and if he could appear in the movie.
He could. Right now it's not something I'm pursuing because I have so much going on in "Avengers" 2. Finding out that Coulson is alive would be an entire B story. And I already have too much movie.
With Captain America: Civil War releasing in May, and the events of Agents of S.H.I.E.L.D. becoming more global by the involvement of the U.S. government and the cooperation by the President of the United States, why not now?
Actor Clark Gregg was asked in an interview during the 2015 New York Comic Con on the connection the show will have with Captain America: Civil War.
Civil War has always been about the registration of superheroes and people with powers. I suspect what we’re doing will connect with that in some way. What I like about what Marvel has done with our show is we explore a broader part of what’s going on in that stuff. Sometimes it connects in a big way. For instance with Winter Soldier, you’re seeing more hours of that dynamic, of suddenly realizing seeing people you’ve worked your whole life for are part of this evil organization trying to kill you, that personal betrayal we get to play out for hours more.
Other than new comers, Marvel has trained their roster of actors with the uncanny ability to provide non-answers to any questions regarding their future and current plans.
He's the director of the biggest government agency in the world, they show up everywhere there is an unexplained event, and so far this season it hasn't been a surprise to anyone that Coulson is still alive.
So why the secrecy? It seems like Coulson is making sure that the news does not make it back to the Avengers only with no real reasoning. Lady Sif made several appearances on the show, and she made the promise not to reveal to Thor that he is still alive. He was the reason for them to come together, but its been three connected movies and three seasons of the show since then.
How they will manage to continue to keep his status secret in the movies will have to be creative, but at this point, there is no reason why he has had no involvement with Netflix's shows.
The first season of Daredevil was about the Kingpin and his attempt to take over Hell's Kitchen, plus the rise of the Daredevil character, but Jessica Jones introduced characters with super human abilities, they shied away from considering them inhuman, and they are not going to call them mutants of course. For some reason they introduced them more as science experiments without leaving any mystery regarding their origins. Which would have opened a door for S.H.I.E.L.D. to get involved in some form.
The show's premise in 2013 was to be a fill in between movies. They also teased and then trended #ItsAllConnected, but since the events of Captain America: Winter Soldier, and the minutes Maria Hill appeared with Coulson before the release of Avengers: Age of Ultron; we've really had no other connections other than name drops and Easter Eggs. Ever since the introduction of the Inhumans, the show has actually been more disconnected from the universe than we think.
If they started to treat Agent Coulson with the current line up of shows and movies as they did during phase one of the MCU, that would be a success. He is bigger than just a TV show.