Okay, lets see:
MODES
1 - Variety - Anyone else noticed how horribly limitating those were in the last Soul Calibur games? You're just fighting either random CAS characters or random regular characters and thats it. Legendary Souls in SCV gave you a "Boss Rush", but its still a glorified Arcade Mode. What happened to modes like Chronicles of the Sword from SCIII? It was an excellent mode, it require some strategic thinking, it had a very cool story, the characters were interesting and you could even relate to them. I want more creative and different modes, not just random copies of Arcade. Tales of Souls were also very good, as you could go on multiple paths and even unlock different things.
2 - Story Mode - Make all characters have relevance. In SCV we only played with 5 movesets there and the story was extremely short (not to mention that the horrible protagonists ruined it). Story should be something cool and engaging and even a bit long.
3 - Arcade Mode - Two things should be brought back for this: Destined Battle custscenes and ENDINGS. I mean, lets be honest, why the hell does an Arcade Mode have no endings? Arcade Mode is supposed to play the role of the classic "character progress if he/she was to reach one of the swords". Even if they are not canon, there should always be something after that, not just a boss fight, you don't even unlock stuff with it.
CREATE A SOUL
Don't get me wrong, Create a Soul in Soul Calibur V was the best it has ever been in the series, but it still has too many horrible flaws.
1 - Costume restrictions - Can someone tell me why the hell some things, like, for example, underwears, are not available for all characters. God knows why they thought it was a good idea to allow Patroklos, Xiba and some characters to wear a fundoshi, but, for some reason, the japanese guy, Mitsurugi cannot select it. Another one which really bothered me, is that the Silk Wrap, an underwear Algol uses by default, is not selectable for him in customization (and neither for Edge Master, Mitsurugi, Siegfried and some others as well). What exactly is different between Kilik/Xiba/Voldo/Maxi/Patroklos/Astaroth/Raphael and Siegfried/Mitsurugi/Edge Master/Algol/Cervantes/Nightmare?
2 - Armor Destruction - You know, its okay to leave armor destruction as a way of letting the fight get sexier as the rounds go, but... can't we have some limitations? We should be able to select what parts of armor we want broken, don't we? While its totally okay to want the sexiness, sometimes its really inconvenient when you end up fighting in a fundoshi for many rounds. Its also horrible that my Link character gets his elf ears chopped off because of that.
3 - Additional movesets - Another thing that was removed from SCIII which I hated, while the additional disciplines from SCIII were not necessarily exclusive, since Bonus Characters used them, at least you were getting something you wouldn't see that often. Having exclusive movesets to CAS adds more variety and makes your created character not be just a copy of one of the defeault movesets. Hell, it would be a really cool thing if they brought movesets from removed characters, like Zasalamel's scythe, or Yun-Seong's sword. This way, while the characters would not be in the game by default, people could still create them and we would have more variety.
4 - Character customization restriction - Why the hell are we not able to customize some characters? I mean, I get not customizing Ezio, because he is a guest character, but what about Dampierre and Lizardman, for example? Why only colors?
OTHERS
DLC - Make GOOD character DLCs, not crap like Dampierre, Dampierre sucks, he is an awful and out of place character. Its a cool thing to have guest character costumes as well, but try not adding just random stuff, some packs have some really random things on them, like why the Loincloth was in the middle of head pieces? Also, make more packs with costume parts from previous games, for removed and remaining characters.
NPC expansion - Some NPCs had quite a lot of potential that wasn't explored in SCV. Some characters like Azola, Marienbard and even others could have a lot more story added to them. Amy was just a Bonus Character before she became part of the main roster in SCIV, this could happen to many others.
Profiles - Bring those back. I want to know who I'm playing with without needing to go to a Wikia, which is not that reliable. Sure, now New Legends of Project Soul has been translated, but how long did it take for that?