I can't match them to anything in the starter set contents, so I guess they must be something more to come (?)
Personally I think the Stormcasts would look cooler if paintschemes were more elemental in nature - like if the armour was made out of fire or ice. I kinda like the idea of them as burning elemental angels, a bit more God's Wrath :D
https://www.youtube.com/watch?v=H9_3WG76cww