The obvious way to introduce Moon Knight is to have him show up as a very minor supporting character in all 4 Netflix minis.
First as Marc Spector, retired mercenary that's being accused of murder and needs Murdock to lawyer up for him.
Then as Steven Grant, millionaire playboy, hiring Jessica Jones to do some detective work for him.
Another as Jake Lockley, a cabby that helps Luke out with a ride.
Then finally as Moon Knight in Iron Fist, as a violent vigilante that takes out someone Danny was after before he could get to him.
Then in Defenders it's revealed that all 4 of these people are ONE IN THE SAME, and that Moon Knight was going after the big bad for defenders, with his 4 appearances being him tackling the same case from different angles from each of his personalities. That way you've got Moon Knight as the connecting tissue between each show, but in a way that you don't realize it until it all comes together.
Shit would be SO cash.