There are some theories about the three remaining season 2 characters that are interesting
Several months ago Project Soul added some characters keynames to the game: stone, yell, star, snow, reptile and yellow. This was after Amy release if I'm not wrong.
Stone could be related to Rock, star to Algol (it's Perseus constellation name), snow to Setsuka due how her name is writen in Japanese, reptile to Lizardman, yellow to Hwang due how his name is writen and yell ... no idea to be honest.
At that moment we didn't know if would be a season 2 but now after the official announcement, I guess these four season 2 characters are among these keynames.
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If we look at the season 2 picture, we can see colours and Soul Calibur / Soul Edge as background for each character.
The first one is yellow and Soul Calibur which could fit with Hwang due it's name and he being a "good" character. The second one, Haohmaru, is red and Soul Edge, which could mean that if he has soul chronicle chapter he could be an "antagonist" in some way. The third one is pink and Soul Calibur and the last one is grey and Soul Edge.
The first one aside is hard to relate all other spots to these keynames but some people think that Haohmaru could be star due being the guest character (because would be way to soon to add Algol to the story).
The last spot being grey could be Rock (stone) but ... having Soul Edge would be off since he always was a nice guy. Due this people think that spot could be Lizardman (reptile) because he also fits being related to Soul Edge (Nightmare team).
The pink one is the hard one to guess. We could guess that he/her has to be related to Soul Calibur and if we asume the other three are right (Hwang/yellow, Lizardman/reptile and Haohmaru as star) that would leave us stone (Rock), snow (Setsuka) and yell (???).
Both Rock and Setsuka aren't villains in Soul Calibur story but the pink color doesn't fit with them and yell is a mystery for me.
We also have the official Soul Calibur 2015 popularity poll to guess which characters can be there:
1. Talim - 862
2. Taki - 720
3. Mitsurugi - 594
4. Ivy - 536
5. Kilik - 536
6. Siegfried - 500
7. Nightmare - 498
8. Zasalamel - 471
9. Yoshimitsu - 454
10. Tira - 438
11. Sophitia - 378
12. Cassandra - 339
13. Amy - 311
14. Yun-seong - 295
15. Seong Mi-na - 291
16. Cervantes - 268
17. Voldo - 259
18. Xianghua - 257
19. Raphael - 254
20. Setsuka - 214
21. Viola - 201
22. Maxi - 199
23. Hwang - 193
24. Hilde - 154
25. Astaroth - 142
26. Z.W.E.I. - 113
27. Natsu - 100
28. Pyrrha - 98
29. Xiba - 81
30. Lizardman - 76
31. Rock - 71
32. Li Long - 65
33. Algol - 59
34. Dampierre - 54
35. Aeon - 52
36. Pyrrha Omega - 45
37. Patroklos - 32
38. Alpha Patroklos - 30
39. Soul Edge - 30
40. Leixia - 28
41. Abyss - 27
42. Charade - 27
43. Olcadan - 26
44. Elysium - 23
45. Edge Master - 15
It had over 10k votes and both Bamco and Project Soul said the would use it as feedback for future Soul Calibur games.
If we look at Tira, Amy and Cassandra, they make sense as the first season pass characters. So if this time we also follow this logic Yun Seong, Setsuka, Viola, Hilde, Hwang, Hilde, Z.W.E.I. and Natsu are the remaining characters that are above 100 votes and aren't still in the game.
I don't think they will add SC V characters due what that game means to the franchise so Yun Seong, Setsuka, Hilde and Hwang are the remaining ones that are somewhat popular.
Both Lizardmand and Aeon are under 100 votes so even if Lizardman appears in the story mode and has an unique style that you can't use (axe and the classic ducking stance) maybe the team think he wouldn't sell enough as DLC character.
In other hand Yun Seong is more popular than Hwang but even if he is named in the story mode, Hwang has an artwork (two in fact if we also count his "Assassin" persona) done, just like Cassandra and Amy.
So after all this info I'm somewhat sure about Hwang being the first one. If I have to guess the other two I think even if the trailer background doesn't fit both Hilde and Setsuka could make the cut due being very popular and the last one could be Lizardman due being already in the story mode but who knows. If I have to bet I would go to: Hwang, Setsuka and Lizardman.