It's funny when you think about it, but despite never being mentioned once, Wilson Fisk has a very lurking presence in The Defenders. He is the one who helped the Hand acquire the lot on which they constructed Midland Circle. Likewise, Karen and Foggy make similar remarks to Matt about him being careless with his secret identity, at a time when we know Fisk is looking into Matt, and that's stuff that's going to play very heavily into Daredevil season 3. (I actually had a theory that John Raymond's plans to destroy Midland Circle were actually him doing Fisk's bidding, as payback against Nobu and Gao, but it was a bit of a stretch)