I am tickled by how very much John occupies the traditional heroine/love interest role.
As Magnussen said (and demonstrated—remember about fire exposing one’s priorities?), he is Sherlock’s ‘damsel in distress.’ He gets to have moments of BAMFery, but he never gets to save the day. He is always the prize. Sherlock wins, he gets to keep John.
And now apparently he is also the leverage/damsel in distress/prize for Mary, as well.
I would love to know more about his relationship with Sholto. Apparently John’s got a long history of forming these sorts of lop-sided bonds with people.