I would love to have Kamikirimusi back, just personally, she was my favorite of the five bonus characters from SoulCalibur IV, but the chance of any of them returning is practically zero. They were all given "something" that ties them to the canon, but you can say the same thing about the guest characters, who have their own goals that involve the swords or the characters in some way. It's not anything special, just arbitrary things to attach them to the universe. Just like Necrid's core is one of Viola's weapons in SoulCalibur V.
@Foot, Siegfried and Nightmare are literally the same person in SoulBlade, SoulCalibur, and SoulCalibur II. SoulCalibur VI has rolled the clock back to SoulCalibur times, so Siegfried and Nightmare are one in the same once again. Raphael and Nightmare were the same person in SoulCalibur V too, and it doesn't stop both of them from being on the roster, so Amy and Viola both being included is just as viable. The thing is, unless they make the story progress faster, further, or differently, then there isn't going to be an opportunity for Amy to become Viola in SoulCalibur VI. At best, we can hope for a non-canon DLC appearance of Viola, but Amy should have no issues being in.
Elysium gets a lot of hate simply because she's a mimic, but she's still quite the unique mimic, not only for the modified Pyrrha Omega moveset, but also her unique Critical Edge which had various applications to the other seven movesets she could use. I believe that it's quite possible that, had SoulCalibur V been completed, there would have been variants of all eight styles, but they could only get Pyrrha Omega's worked in to fit the cloning Sophitia idea. Soul Calibur being a lawful good absolute, going to any stretch to accomplish its goals, is a very cool idea with a lot of potential, but it's doubtful that it will return in that form due to everyone hating the three mimics. Soul Edge just wants to eat souls, Soul Calibur just wants to destroy Soul Edge, simple enough ideas, sure, but the way they went with Elysium, if it could shapeshift into many forms, would be a very cool take on the mimic instead of just being Edge Master.
Hilde has the same problem as Viola, that unless they change the story events, they'd have more difficulty working her in, since they mostly seem to want to keep the story the same, despite the reboot doing things differently possibilities. The more reasonable approach, I think, would be to introduce Salia as a playable character, with a simpler (as she would be less skilled) variant of Hilde's moveset. Perhaps while in Soul Charge she could unlock the advance techniques such as charging attacks and have more combo potential.
Talim is most assuredly going to make it in, as far as we're led to believe that they're taking that Facebook character poll seriously. Cassandra seems like an easy add, too, so I'm not too concerned about her not making it in. I'm hoping that the leak saying Seong Mi-na not making it in was false, but it's always possible that she will be added in as a DLC character, which, as long as she does make it in, I'm happy.