[SPOILERS for Daredevil season 2 ahead.]
Matt Murdock/Daredevil, Jessica Jones and Luke Cage have all now made their debut in the Marvel Cinematic Universe, as part of the Netflix corner (which is based in New York) of Marvel's shared movie and TV show universe. Danny Rand/Iron Fist will see his own Marvel/Netflix solo series debut in the first quarter of 2017, before he and the other three street-level superheroes of Hell's Kitchen (and Harlem) join forces during the miniseries, The Defenders.
Production on The Defenders is currently underway and Marvel/Netflix has taken to confirming returning supporting players in the miniseries (via the official Defenders Twitter account), before they are "discovered" via leaked photos from The Defenders' set. Among those Daredevil, Jessica Jones and Luke Cage TV series players confirmed for The Defenders are Foggy Nelson (Elden Henson), Trish Walker (Rachel Taylor), Misty Knight (Simone Missick) - and now, Daredevil season 2's Elektra Natchios, once again played by Elodie Yung.
A video confirming Yung's return as Elektra in The Defenders was posted to the miniseries' official Twitter account. The video includes the tagline "The Strong Survive" with Elektra, but it does not elaborate on her role in the Defenders' storyline beyond that.
Daredevil season 2 concluded with the revelation that Matt Murdock's (Charlie Cox) old flame, Elektra is in fact Black Sky: a deadly "weapon" forged by The Hand, for reasons that have yet to be revealed in full. Elektra was killed not long after this reveal, but the final shot of Daredevil season 2 showed Miss Natchios about to be resurrected by The Hand; setting up for her to potentially return as an antagonist in The Defenders. It's been speculated that when Elektra does come back, she will possess dark supernatural abilities and be powerful enough to necessitate the street-level heroes of New York coming together and saving their city from her and her mysterious "boss" (Sigourney Weaver).
None of this has been confirmed yet of course, but who better to serve as the "muscle" for Weaver's character on The Defenders than a character whom viewers already know from Daredevil season 2 - and whose turn to evil would bring out conflicting emotions in Matt Murdock, especially? Having the magically-empowered Elektra serve as an antagonist in The Defenders would also play out as a natural progression of the overt supernatural elements from Iron Fist season 1; at the same time, it would more closely tie-in the events of The Defenders with those from Daredevil in particular.
Plus, if Elektra is an antagonist in The Defenders, then both she and Weaver's character should have The Hand under their command - and the only thing powerful enough to protect New York from such a deadly threat would indeed be its finest everyday superheroes (with a little help from their friends).
Daredevil seasons 1 and 2, Jessica Jones season 1, and Luke Cage season 1 are now available on Netflix. Iron Fist will premiere on March 17, 2017. The Defenders and The Punisher will arrive in 2017. Premiere dates for the newest seasons of Jessica Jones and Daredevil have not yet been announced.