I love threads like this. :D
Ok, my personal wishlist for the next Starguardian team are:

I want to discuss what kind of characters/roles I imagine for them. ^^
Caitlyn
Classical class representative, highly intelligent and responsible. These talents make her the obvious choice for the leader of the team as well. She and Vi are best friends, many people don't understand that, since their personalities are total opposites. I could even imagine some romance being hinted here. The Starguardians could use some sweet yuri.^^
Has one familiar, who heavily enjoys sweets (especially cupcakes).
Vi
The bokukko or tomboy, always wants to have a good brawl. She enjoys the fight, but she would give her life to save her friends. Like mentioned, best friends with Caitlyn. She thinks that Caitlyn is taking everything too serious and that she is burdening herself too much. She wants to be her vent, wants to enable Caitlyn to have some fun and enjoy herself.
2 familiars like Jinx and Miss Fortune, they transform into her gauntlets.
Quinn
Tsundere, always acts annoyed by her team and claims that she would prefer to be let alone. But that is actually not true, she grows to like her team, but she would never tell them, that would be too embarassing. Her familiar is obviously Valor. Valor enables her to fly in the sky, I think that she and Ezreal could have an interesting encounter because of that.
Orianna
The Rei Ayanami Expy. She was a terminally ill girl, but the first star granted her a new body so she can survive. But this robot like body kinda seperates her from the normal society. She is not able to visit the school like the other team members, instead she is doing the housework together with her familiar (the ball). She feels lonely because of that, but you can't tell on the first sight, since her personality is kuudere, she seems pretty emotionless (another side effect of her new body).
Taliyah
Traditional himedere, she was born in upper class and behaves like that. She doesn't understand why she isn't the leader of the team, since it should obviously be her "birth right". Her clothing should be traditional japanese (fits well with her sleeves). She has one familiar.
Bonus Round!!!!
While I would enjoy seeing this new starguardian team, giving another team after Ahri's might be a bit much and Riot probably wants to take a break from new teams. My solution: Next round could be a team of villains, Fallen Starguardians!
For everyone who knows the series: They would basically be witches from Puella Magi Madoka Magica. They used to be Starguardians, but cruel fate transformed them into their enemies and now they try to do the same to the current Starguardians. Syndra could even join them in another story episode!
My choices for that evil squad:
They corrupted their familiars and some fuse with them!
Lissandra
The oldest Fallen Starguardian and therefore the leader. She was facing the truth that every star has to burn out someday and die (burnout -> her being cold, nice symbolism). She refused and embraced the evil side of hers, turning her back to the first star and trying to "save" as many Starguardians as possible by giving them an alternative so they can live.
Elise
Her familiar is a spider and she is able to fuse with it for her spider form. She admires beauty more than everything else and wants to make the Starguardians her subs, she may even be a little bit perverted. She just wants to unite all these cute girls under her.
Illaoi
Her familiar is an octopus she uses as her idol. Strength is all that counts for her, Lissandra was able to grant her that strength. She wants to gift it to the other Starguardians, telling them that it's not about "good or evil", since these are just perspectives. The strongest is always right.
Sejuani
The most likable in the team. Her entire Starguardian team died and she didn't want the same fate for her familiar Bristle and herself, therefore she obeyed Lissandra and her power. She actually disagrees alot with Lissandra and is jelous of the Starguardians, being able to live the life she wanted to with her old friends.
Shyvana
Basically just driven by hatred. She felt betrayed by the first star and her actual goal is to destroy it, to bring an end to this system. Would probably even challenge Lissandra to became the new leader of the Fallen Starguardians, if it turns out that Lissandra isn't willing to destroy the first star like she wants to. Her 2 familiars are transforming into her gauntlets, they look like dragons and she is able to fuse with them for her dragon form.