I would like to see:
1. as little of Mary Morstan as possible...my thoughts are that if John and Mary Morstan get married and she dies (in the books) between "The Adventure of the Final Problem" and "The Adventure of the Empty House" when sherlock comes back that she doesn't have to really be in the tv series at all
2. Mycroft interference more often, sibling rivalry...show where Mycroft lives or something about sherlocks family...some sort of awkward event at the family home
3. sherlock to come back earlier than three years down the road. Maybe john can just get engaged and then break it off or preferably she can break it off because she feels neglected
4. No sherlock and john hook up - I like it like a non sexual romance, but not a bromance in the more platonic sense. nothing needs to be addressed but johns feelings should be evident. I think they have been but some news stories don't reflect what I see.
5. John has to stay at Baker street...there can be an assumption of recognition that he moved out when he thought sherlock was dead but he has to move back in (preferably no episodes where it shows him living elsewhere)
6. John needs to punch sherlock out for leaving and sherlock needs to understand the significance of his anger on some level...ned to make clear johns grief..if you have to introduce Mary as the comforter, do it and get it over with quickly...he needs to recognize quickly why sherlock did it
7. Sherlock needs to express some form of sorrow even if he doesn't know its sorrow or regret...some form of emotion toward the pain...not that he caused it because he was saving their lives... but that it happened
8. if we have to have the whole mary wedding, can we not make it an episode but just something that happens in the background