Halley Berry kicks ass as Sofia, but you can also see that she's been out of the life for a little bit compared to John. She's definitely set up to be a barrier for him though, because you know that there's no way that he can go up against her and her dogs emotionally, but he has the leverage about her daughter that puts him in a position that's also uncomfortable for him emotionally. I absolutely expect them to deliver on that development from Casa Blanca.
The Russians. It's VERY clear that he burned his one and only ticket with them, and that's going to cost him somehow. I'd fully expect the cause and effect from them to come back with a particular vengeance. I'd expect that we get to learn a bit about John's history with them as the reasoning.
Winston is far more dangerous and smart than he ever let on. New York is his, and he's always negotiating for his own safety and power, even while he considers John a good friend. He's playing chess (literally in the reveal shot) to turn John's actions into his own opportunities, likely because he's attempting to secure a way to get himself closer to the High Table. Additionally, we know how much of a badass Charon is.
With The Bowery King, John has what he needs to be a force from the shadows that also threatens what's happening with Winston, but potentially to be double-crossed again. John needs some genuine backing to help him out to kick this one off differently, and this is the shady underbelly that is perfectly suited for that, especially if we're seeing John return to being the Baba Yaga for any period of time – necessitating finding himself again.
The Elder has his wedding ring, setting the stakes of the need to return there to reclaim himself as John Wick and not as the Baba Yaga. But then that presents the issue of a power vacuum, with so, SO many parties looking to fill the position. If John wants out of that life, it likely has to involve dismantling the whole system, or relegating that he's trapped into the position he wants least of all, Conan-style, as a king himself. He'll have the ring back, but no finger to wear it on.
It'll be really interesting to see how they ultimately handle that, since it's clearly also a film series written to be deeply cathartic for Keanu Reeves personally, given his own past with loss and pain. I'd expect that they know where they ultimately want to take it because of that.