Here are a couple of villains I'd like to see the various Marvel/Netflix shows tackle over time. These are only characters that haven't been addressed or referenced already in any of the Netflix shows (so characters like The Owl or Steel Serpent don't count).
List will probably change over time.
Daredevil's second biggest rival, enemy of Elektra and one of the deadliest fighters in the Marvel universe. Bullseye is a must-villain for Daredevil's series.
Young, traumatized, superpowered woman who escaped an abusive relationship and has to deal with mental illness? Sound familiar? Typhoid Mary would make an excellent foil for Jessica Jones to fight.
With the premiere of Iron Fist and Doctor Strange, we will officially be introduced to Marvel's magical side. I personally think it would be awesome if the writer's took advantage of that in order to insert more magic in Netflix shows as well. The Hood is also an ideal villain, since he is both menacing enough to be an enemy of The Defenders, but also fits as a foil for Luke Cage (both were convicts that received superpowers), or as a villain for Iron Fist (they both have mystical origins and Iron Fist needs more villains). He is also connected to the Kingpin.
In the MCU, Marvel has mostly skirted around the idea of how Superheroes affect normal crime. Now that superpowered individuals are also going after "normal" criminals, it'll be fascinating to watch how a powerful crime organization like the Maggia will have to adapt in order to challenge heroes like Luke Cage or Daredevil.
(One of the) heads of The Maggia, who has fought Jessica Jones, Luke Cage and Iron Fist before. Is infamous for associating with supervillains and employing mad scientists, which would make him much more interesting compared to other Marvel crime lords. Count Nefaria also has superpowers, meaning that he can also serve physically as a threat.
Taskmaster's copying powers would make him a formidable opponent to martial arts-based heroes like Iron Fist and Daredevil.
A sadistic, rock-skinned criminal enforcer, Tombstone would be an excellent enemy for Luke Cage.
