In an interview with Collider, Luke Cage was asked if he was excited about the scenes between his character and Iron Fist, Luke Cage's best friend, to which he replied:
"The actor has been cast, but he’s in a basement somewhere. When the time is right, they’ll let him up and tell him where he is. I am [excited]. I’ll get a nice little break, after doing Jessica Jones and Luke Cage. Whether I’m in [his show], I don’t know, but there’s The Defenders."
So it looks like Marvel is just waiting for the right time to announce the casting. It should be noted that Ryan Phillipe has reportedly been in talks with Marvel for the role, and other beige names like Alain Moussi have also been thrown around in the rumor mill regarding the casting.
Don't get your hopes up, ONTD!