I suggested this in another thread but: Could you also make a female Nali too? We know they exist because of Vandora and various others. Of course, they would be brown like their male counterparts. Vandora is blue because she's immortal.
That "Reborn" Nali should be blue too, no? Could add wings as well since Vandora has them.
Also, I bet if you played with their models a bit the Krall and Mercenary races might be possible (remove the Mercenary gun arm/remove Krall staff). Unlike the Skaarj, the Krall and Mercenary aren't hive based races, so female counterparts could be created for them too. Mercenarys are lizardlike, so they wouldn't have breasts, but a female would probably have a thinner frame, more curvature, and would have larger hips than shoulders. Of course, this should be common knowledge for artists. Maybe I'm thinking too ambitiously, though?
For Sonya I was actually thinking you could make the shoulder plates more like in Unreal 1. Ash looks good, and it would be interesting to see Ivan and Kristoph.