Don't know if this is still being updated, but I'd suggest Chel, from the Road to El Dorado, as a medium addition.
Hepzibah (with the Corsair), Scarlet Witch (with Quicksilver), Dagger (with Cloak, 2013 Ultimate editions), Mythic Cassiopeia
Chosen, In Planning:
Carmelita Fox (with Sly Cooper), Riza Hawkeye (with Roy Mustang), Red (with Subject Unknown)
Ravager, Emma Frost (with Namor, Phoenix Five editions)