Wouldn't it be awesome if at one point there's a showdown between John and Mary like the one in TRF between Sherlock and Moriarty?

“You’re insane.” “You’re just getting that now?” YES, GIVE IT TO ME

Also, imagine if we get this throwback to The Great Game: John aiming his gun at Mary, while Sherlock watches with wide eyes. John whispering, “Let him go, or I will kill you.”

If we thought The Abominable Bride version of John was BAMF, just wait for series 4…