My guess at the new champion: A "spirit of the land", like an "Anivia of the south"

Going by the color sheme it looks pretty Shuriman to me. At first I thought it would be something demacian, as the whole angel thing flies pretty well with them, but for that the light would be more pale and white.

Then I thought it might be the Kayle rework. And yes, even if we just got Galio this might be a thing, given how fast Riot can pump out stuff when the stars alling. Remember Gnar? In the patch right after him there was instantly Azir coming like "SHURIMA WAITS FOR NONE" and rushed into the PBE (full of bugs tho).

But then again the asymmetry in the teaser seems to be unfitting for Kayle, so instead it makes more sense to assume an entirely different character.

Let's see: sun symbolism, shurima color palette, bird, a certain duality given the asymmetry (desert areas are kinda two faced if you think about it. Burning hot at day, cold as the winter at night. An oasis overflowing with life, and the liveless ocean of sand) - all in all it might fit into the narrative of a "Shuriman Anivia).

Now the only question would be why she's humanoid... maybe because the impact of mankind in Shurima is bigger than in the Freljord? I mean, they already had an empire while up north they were some barbarians with ice powers - and the iceborn were not human anymore, that much can be said. Or maybe it has something to do with the sun, as there is just a lot more energy in this area of the world? I doubt that the technology of the Sun Disk would work up in the north for example.

But then again this golden orb DOES kinda look like a Kayle ult, so I am not 100% certain...