Black Widow

It may be a bit of a stretch to think that someone of Scarlet Johansson's calibre could show up on Daredevil, but anything is possible in the MCU. The character has been a major player in many of Daredevil's adventures and is also one of his more famous love interests. We're not saying that she has to have a multi-episode arc (though that would be nice), but some kind of allusion to her history with Matt would be appreciated and could help transition Daredevil into the feature film side of the universe.