I'm 99% certain development for the next two sprites is already well underway (if it isn't, I'd be concerned!) but I'd still like to throw out my ideas regarding the sprites. Many players have many ideas for the green/blue sprites, all of which I find awesome. I try to focus on the mineral lore and such for these two sprites...these links lead to lengthy explanations of abilities and appearances:

-Blue Battle Sprite
-Green Battle Sprite

In short:

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Blue: owl form, shock based attacks, focuses on technical improvements.

Inspiration: Bubo, Athena's Owl, and Owls are associated with wisdom/knowledge/the night, and that's what moonstone is -knowledge, traveling worlds, TARDIS, doctor who, blue. Wee!

Harnesses: all but piercing.

Moves:
1) storm-driver like, nullifies one attack of any enemies hit - 2-4 enemies max per sprite. Regular devilites wouldn't be able to attack at all, etc. Ults: shock (2 projectile splits), OR more splitting of projectiles (4 projectile split).
2) mechanic know-it-all, modifies pickup buffs to last longer. Ults: can pick up two buffs and make them last twice as long, OR one buff and have it endless.
3) either a nitronome pushback effect, OR a vortex sucking effect - shock or ice depending on ult chosen (shock push, ice vortex). Ice is cold, so is space!
*Note: though stars and such are not very cold at all.

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Green: silkwing-bug form (dragonfly like, with spider-like hints), variety of status effects, focuses on Healer manipulation and life+death together.

Inspiration: silkwings and valestone's description.

Harnesses: all but shadow.

Moves:
1) a net that acts much like freeze status. Ults: DoT for the targets in the web, OR have the web ignore shields of enemies (otherwise acts normal). Of particular note: attacking enemies in the web doesn't break the web, unlike freeze. Single or two target only, but very powerful effect.
2) mender manipulation - stops them from healing. Ults: causes harm to enemies, OR restores the squadmates a total of 5 hp depending on conditions.
3) bug swarm - causes enemies to take damage from anything, and negates a variety of effects (such as zombies turning into revive-able skulls, they just die even if they're in a totem/deadnaught radius, etc.). Ults: enemies target each other actively, OR are inflicted with random status. This one marks targets in a similar fashion to the Mask's ult.