I know we wont get more guardians for probably a year, but my friends and I like to play all skin theme teams and we’ve found a severe lack of top and jungler Star Guardians. In fact Poppy is the only one, for both roles, of which she does ok...
Can the next iteration expand a bit of those roles? Its easily one of the best lines but has the least diversity
Star Guardian Vi should be a thing, with 2 familiars transforming into her gauntlets. She should get released alongside Caitlyn, tho, simply because they are a lore team and should stay a team in Star Guardian.
Top lane is a bit harder to pick something for, since the champion pool for this lane is dominated by males.
Some possible candidates:
From these, I would consider Kayle the best choice.
I always thought there were a few obvious picks for tanks/general top and jungle picks. 
fit aesthetically well and make a good pair as always. Someone mentioned , who naturally pairs well with 
and makes for good team dynamic. 
have a lot going on design-wise that would look nice in the Star Guardian style, and their character dynamic lends itself to stories or conflict. 
is an old favorite for this pick, and his familiar could attach to the people he Ws, plus visually his shoulder...gems could look great as stars. I also see 
a lot, usually paired with 
, who each are primarily midlane, but have some viability in top (for Ekko at least) or jungle. Their youthful attitudes make them good picks, and I think fans of the characters might enjoy the SG thematic for them.
Along with Morgana and/or Kayle, there are countless good villainess picks; while I think Zoe ended up working well, we also have picks like 
(Cass is typically a mid, but can be played top too) 
. Xayah's spitefulness ended up working well for the corruption angle, and I think other Champions like 
could work in a similar manner.
There's always the potential for a Champion to represent the First Star, the one who gives the Star Guardians their powers and deems them worthy. I still think 
is the top pick for this, but I think someone like 
with his unusual design and natural kindness could work, too.
And lastly, we have my usual oddball pick 
; he's among the younger crowd and has a built in familiar with Rhaast. He's also a solid jungle pick that provides some flexibility with his choice between Shadow Assassin (another class they have none of) and Rhaast's more bruiser-ish qualities.
These are just a few ideas off the top of my head. There are some candidates I didn't include (like Karma or Tristana) since they weren't really top/jungle/tank picks (although thinking on it, I guess Karma could work top, too). I definitely agree it would be nice to get some role variety for Star Guardian teams to work better, and so they don't have to rely on Poppy so much.
Top lane star guardian: 
Is Taliyah still played Jungle? Make her a star guardian, there's a ton of cool concept art of her out there already, seriously check it out, just type Star Guardian Taliyah in google and you'll find tons of it.
Would make for some fun Star Guardians.
Neeko is played top
Probably an unpopular opinion since she already has a metric fuckton of skins but I'm honestly still waiting for a Star Guardian Annie,
I mean come one, look at these concepts;
https://i.pinimg.com/originals/4d/37/0a/4d370a10f4232ee057b46e9b3fc09978.jpg
https://i.pinimg.com/originals/25/37/3d/25373dfd65a7a079c01f01aad3faa2ae.jpg
Xayah is a surprisingly good jungler. Not meta, but not bad.
This is why I think SG shen as Tuxedo Mask would be great
Star Guardians until Season 3 are color-coded to roles. It sounds dumb but once explained you'll understand.
Top-lane is purple, thus top lane is Janna and Syndra. I've played both at top countless times. It's almost like a mid fill lane, and Janna mid works out fine so there's no real reason for me to explain further.
Jungle is where the meta-slaves want to eat my ass. Junglers are blue, being Poppy and Ezreal. "Nuh uh nuh uh, dumb iron 4 hardstuck b*tch; Ezreal no jung" Back when SG Season 2 was up, even beforehand; Ezreal jungle was rising in popularity. It became a meta until the balance team nuked it. And even then, it was used as the key build of the Faceless in the trials event. And if you don't believe me just look up Ezreal Jungle montage.
Mid is pink, being Ahri and Lux. Nothing more to say here.
ADC is red, being Miss Fortune and Jinx. Again, self explanatory nothing to say. And green is support, Lulu and Soraka.
Now if we turn to Season 3, trying to still use the color based role system... oh holy FxxK they screwed it up. Neeko is green with hints of orange ( MF's secondary color. ) This puts her between Soraka / Lulu and Jinx / MF. This could be a hint to how Neeko ADC is a meta but it still ruins most of the appeal.
Xayah, when not consumed by darkness is PINK. FXXKING PINK. Since WHEN are Xayah and Rakan in midlane? Rakan when not consumed is green thank GOD.
And last but not least is Zoe, which makes sense since the guardians with dark history ( Syndra, and Janna's mysterious past ) are at top lane, and Zoe is purple. #TankZoeAnyone?
are the answers.
Star Guardian in the jungle.
100% agreed. (Even though I'm really happy about the fact that almost all my mains have Star Guardian skins now :D!)
Actually, I think most of the main skinlines lack skins for tanky top/jg champs. (Blood Moon, Arcade, Star Guardian).
Top/JG champs that could work as Star Guardan: Irelia, Riven, Kayn, Ekko, Kayle, Diana, Xin, Fiora, Vi, or even Wukong.
Kayn would be cool because Blue Kayn could turn Star Guardian and Red Kayn could turn Fallen/Corrupted Star Guardian like Xay/Rakan.
Technically, any of the Star Guardians could work as a cheesy jungle pick, but it's true, there aren't really any good jungler Star Guardians.
And as for top laners, even though there aren't a lot of tanky champions who could fit the Star Guardian skin line well, there's an easy way to get around that: give us Star Guardian skins for some of our tankbusting assassins. Katarina, Fiora, Riven, Akali, Irelia...I mean, all of these are popular champions whom I'm certain will get Star Guardian skins eventually, but it's still strange how Poppy is still the only toplaner in the skin line.
Hopefully for the next full team we'll get a team that can actually work in a composition like Team 1, and not get another Team 2 which had two midlaners and no toplaner. And even when one puts Ahri's previous team together, there's still two midlaners and no toplaner. Maybe it's a weird quirk she tends to carry when she gathers teammates? [sg-miss-fortune]
I've been preaching top / jungle / tank Star guardian girls.
Primarily
Thanks for all the responses! I think my favorites for some champions are (and im only focusing on the two lanes since I feel the others have obvious choices and already have plenty):
Top: and for a male i'd go with (Nice, positive male figure and kit and his spirit blade can be his power-channel).
Jungle: (Villain), and unpopular opinion i'd say , (her theme is already awesome by itself and her power can be in wolf) and for a male (Villain) or maybe (hero, but he doesn't really fit the star guardian aesthetic, but I think he's hot so would love to see him in costume, lol)
I know this sounds weird and completely out of place, I would love to see Darius because I am a main and he would probably fit into this dark star guardian lore... Maybe I am wrong.
I don't really think any skin line is really made with a champions role/Lane in mind. Most have been chosen to flow with a certain story they want to tell / express.
