2. Watsons Wife
We want to see the tension that the character of Mary would cause between Sherlock and John. Weve already seen how Sherlocks demands wreak havoc on Johns love life in the past, but weve yet to see how a more regular presence would react to the expectations Sherlock has of John. Cases frequently require hitting the streets for an entire night, not to mention life threatening danger. Not many significant others will be happy about their partners risking their lives for no pay with no benefits other than a really awesome blog post. We want to see what happens when John cant get out of his responsibilities to Mary and Sherlock has to go solo. This will also help with the first concern.