Marvel properties are unique in their level of interconnection. Sure, he haven't seen Foggy Nelson or Melinda May in a movie alongside Captain America yet, but within their respective worlds, the characters tend to crossover. The most persistent force in the Marvel Netflix shows has been that of Madame Gao, the mysterious leader of the Hand, who has menaced both Matt Murdock and Danny Rand in their respective shows. Although actor Wai Ching Ho hasn't yet appeared in promotional material, it seems that the mysterious villain will be appearing in The Defenders.
As reported by MCU Exchange, Mike Colter and Finn Jones (Luke Cage and Iron Fist respectively) spilled the beans in an appearance at Comicpalooza in Houston when they were asked which characters would be appearing in The Defenders. Marvel actors are given a very short leash to disclose that sort of information, so Colter and Jones were careful only to mention characters that had already appeared in the trailers. That would have been the end of it, until a member of the audience shouted out "Madame Gao!" which Colter quickly confirmed.
Though not an official confirmation from Marvel or Netflix, Colter's admission is most likely accurate. From the trailers, it looks like The Defenders will have the four Netflix heroes and their allies team up to fight the Hand, which Madame Gao has represented across the shows. We know Elektra will be making a return, and Sigourney Weaver will be taking on the role of the main villain, but Gao's absence would be quite notable.
Executive produced by Douglas Petrie, Marco Ramirez, Drew Goddard and Jeph Loeb, “Marvel’s Defenders” arrives on Netflix August 18 2017 and stars Charlie Cox, Krysten Ritter, Mike Colter, Finn Jones, Simone Missick, Elodie Yung, Deborah Ann Woll, Elden Henson, Carrie-Anne Moss, Eka Darville, Rosario Dawson, Rachael Taylor, Scott Glenn, Jessica Henwick and Sigourney Weaver.