2. Why Would Black Siren Think She Could Blackmail Emiko Over Ricardo Diaz's Death?
When Black Siren confronts Emiko over her murdering Ricardo Diaz, it's clear that she has blackmail on her mind. She speaks with mocking concern about how she knows how that Emiko has endeared herself to both Oliver and his team. She then says that "family dinners are going to be a little bit more awkward" if they were to find out that Emiko had killed Ricardo Diaz in cold blood.
It's unclear just why Black Siren thinks this would be the case. Not one week earlier in "Brothers and Sisters," Black Siren was helping Felicity Smoak to facilitate a plan to kill Ricardo Diaz. Later in the episode, when Oliver realized what was going on, he said that he wouldn't stand in the way of his wife's actions and that he would trust her judgement if she felt that Diaz did need to die in order for them to be safe.
While Oliver Queen may talk a good game about not killing his enemies and trying to turn over a new leaf from his early days as a more violent vigilante, he's also developed just enough awareness to be aware of how hypocritical it's for him to lecture anyone on killing in the name of revenge. As such, his response to Emiko killing Diaz would probably be to offer her support and an ear if she felt the need to talk about it. The rest of Team Arrow, with the possible exception of Dinah Drake, would probably be the first to buy Emiko a drink for finally ending the threat that Diaz posed once and for all.
1. Where Do Felicity's Coordinates Lead?
Most of the flash-forward sequences to Star City 2038 this week focused on the developing relationship between Mia Smoak and William Clayton. The two only recently learned of their status as siblings, with Mia apparently having been raised in secret with her existence being kept from all but her father and mother's closest friends. William Clayton was similarly isolated, his grandparents having apparently thwarted all of Oliver and Felicity's efforts to reach out to him over the years, causing William to grow to adulthood thinking he'd been abandoned by his father and stepmother after his grandparents won custody of him.
When the two lost scions of the Queen family finally locate a mini-cassette player capable of playing the tape that Felicity had left hidden for them inside of her Rubik's cube projector, they find a message. In it, Felicity apologizes for keeping the two apart and for having made a mess of their lives, though she does say it was ultimately necessary to keep them safe from her and Oliver's enemies. She then gives them a set of coordinates, with the instructions to pass the location on to Star City's vigilantes before getting as far away from Star City as possible. Naturally, Mia and William agree to ignore that final instruction.
Mia recognizes the coordinates and says that they are somewhere inside the Glades - the gated community in the center of Star City in the future of 2038. She doesn't say what the coordinates lead to but she does say that they are going to have to go into the Glades in order to get bottom of the mystery behind Felicity's whereabouts and the bombing plot that could destroy all of Star City outside the Glades. Doubtlessly, the effort to sneak into the Glades will lie at the center of the flash-forwards in the next episode of Arrow.