They've tugged heavily on a connective thread between Iron Fist and Daredevil, with the Hand / K'un-Lun connection, so I feel like that's been done.
That leaves us with another connection yet to be explored, the chemical company that is responsible for Matt's blindness and Jessica's powers, and *may* be soft-retconned into being somehow connected to the experiments being run on prisoners that gave Luke his bulletproof skin, as well. Having to face *multiple* threats with Jessica/Luke class strength and toughness, working for the evil chemical company (which is far more than just an evil chemical company, but a kind of 'Power Broker' producing metahuman enforcers), could be one way to amp up the tension, particularly for Matt (who isn't generally able to fight on that level, and will have to even up the odds by turning out the lights or something), but also for Danny (who can't take punches like Luke), or Jessica (who has already mentioned how she doesn't know martial arts, and would be hard-pressed against foes who have her strength *and* are trained in hand to hand).
Add in some potential use of chemical weapons (given who they are working for), or even someone with powers related to chemicals, such as acid skin, and there's possibly enough fodder for an entire season with zero Hand / ninja / K'un-Lun ties.