The characters with more chances:
Ryu, Ken and Chun-Li. There’s no discussion these are going to be in the game.
As for the others, in order, these are the ones with higher chances:
Guile. In fact, I think there are high chances he could be a playable character, Charlie might come back as a secret character or a mid boss or perhaps even a boss, but I think his gameplay will be changed this time. If it is not and Charlie is Guile in this game, Guile may comeback in an update, but I think they’re going to change Charlie’s gameplay anyway.
Bison. He has a very unique gameplay, and he’s important for the story. Super high chances.
Zangief. He’s the quintaessential grappler, I’d be nothing surprised he makes up the cut, but I would really like another grappler to take his place.
These have mid chances:
Balrog. I would say retire him, but his ending in SSFIV seemed to be leading to something else, so there’s a middle chance we could see him back.
Dhalsim. He seems to have a strong fanbase/userbase, as for myself I find it really boring and I don’t think he could work in a more offensive game like Street Fighter V, they should replace him with Necro, but Necro has never been too popular.
Sagat. He’s really popular, but not that necessary. And it seems like they gave his storyline a closure in Super Street Fighter IV, maybe they had planned retiring him.
Vega. His gameplay is truly unique, although he has become less effective with the passing of time. I don’t really see anyone else replacing him, not even Rolento, so there are chances he could be in, but also he’s really nothing important for the storyline, and remember Shadaloo was supposed to be dismantled, so having back the four bosses again wouldn’t make much sense, so maybe they will skip him.
These have low chances, in my opinion:
Blanka and Honda. They are the least favored of the original 8, they didn’t show up until Alpha 3, for example, so I’d say they’re the most disposables from the cast. Their gameplay is not really that unique and they could be replaced. But if the other original 8 are included, they will almost forcefully appear.
Cammy. She has been central in many sagas like Alpha, II and even IV, I think it’s time to give her a race, her gameplay’s good for games like SFII and IV, but I always found her a little lacking and I don’t think she could adapt.
Fei Long. OK, they gave him a proper come back in Street Fighter IV but he has been really spoiled since then. I picture him being replaced in favour of Karin or Yang.
**Dee Jay and T. Hawk. **You gotta be kidding me. These guys have basically zero chances.