Relatively attractive by default.

Body needs to look human, and represent the gender its supposed to be fairly well.

Needs to be well constructed without crazy weird joint issues, or asymmetrical mesh problems, and UV maps that actually exist for ALL body parts and that don't overlap, that can be textured relatively easily. 

Versatility. 

Versatility means LOTS of morphs.

The majority of vendors are not modelers, they're dial spinners. 

If you want a vendor to support a figure, give them enough morph dials to choke on. And then give them some more.

If you're expecting them to create their own morphs you're going to be waiting a long time. About as long as it takes for the V4, V5, V6, V7, V8 and probably the V9 markets to dry up.

 

~Shane