Defenders are definitely happening. You can't have 67 fricking characters and not include any Netflix heroes.
Nobody said we're getting 67 characters for sure. They said they have a board with 67 characters. That could just as easily mean they're trying to decide who will or won't make it into the films. But even if it's true and we're getting 67 characters, it's not hard to reach that number without dipping into the TV shows.
Assuming nobody dies in Civil War:
The Avengers: Iron Man, Captain America, Hulk, Thor, Black Widow, and Hawkeye.
The Guardians of the Galaxy: Star-Lord, Gamora, Drax, Rocket Raccoon, and Groot.
The New Avengers: War Machine, Falcon, Scarlet Witch, and the Vision.
Confirmed Civil War heroes: The Winter Soldier, Ant-Man, Black Panther, and Spider-Man
Confirmed Phase 3 heroes beyond: Doctor Strange, Mantis, the Wasp, and Captain Marvel.
The Inhumans: DEFINITELY will include Black Bolt and Medusa. Karnak, Lockjaw, Gorgon, Crystal, and Triton are very likely as well.
So at least 30 heroes.
So villains: Thanos for sure.
Past MCU villains who are still alive: The Abomination, the Leader, Nebula, Justin Hammer, Loki, Batroc, and possibly the Red Skull.
Confirmed Phase 3 villains: Baron Zemo, Klaw, Mads Mikkelsen's character from Doctor Strange, Baron Mordo, whoever will be the Ant-Man and the Wasp villain, whoever will be the Guardians of the Galaxy 2 villain, whoever will be the villain of Thor: Ragnarok, whoever will be the villain of the Captain Marvel movie, and Maximus the Mad (likely).
This is a toss-up since a number of them will likely die, but probably not all of them.
Then look at supporting characters from each franchise:
The Hulk: Betty Ross and Thunderbolt Ross.
Iron Man: Pepper Potts and Happy Hogan, possibly even Christine Everheart (she did appear in those viral Ant-Man segments).
Captain America: Sharon Carter, Peggy Carter (flashbacks), and Howard Stark (flashbacks). Possibly even the Howling Commandos (flashbacks).
S.H.I.E.L.D.: Nick Fury and Maria Hill.
Thor: Heimdall, Lady Sif, Volstagg, Fandral, Valkyrie (rumored to appear in Thor: Ragnarok), Jane Foster, Darcy, Professor Selvig, Darcy's boyfriend (I forget his name).
The Avengers: Helen Cho. Hawkeye's wife and three kids.
Ant-Man: Hank Pym. Possibly Janet Van Dyne (if she's rescued in Ant-Man 2), Scott's heist crew (Dave, Luis, and Kurt), Paxton, Cassie Lang, and Maggie.
Guardians of the Galaxy: Yondu, Irani Rael, Rhomann Dey, Cosmo, and the Collector.
Black Panther: T'Chaka (flashbacks) and depending on who else ends up in the film, possibly T'Challa's sister Shuri.
Doctor Strange: Night Nurse and the Ancient One.
Whoever end up as the supporting players in Captain Marvel.
Other: Howard the Duck and Martin Freeman's mystery character.
As you can see, the MCU has a very deep bench of characters without digging into the TV shows.