The one thing that is needed, IMO, is a figure that can take a greater range of positions without deforming badly. V3 is streets ahead of V1-2, Posette, Eve etc in that regard, but still rather lacking.

But I would also suggest it should be essential for a new figure to be able to use the large amount of materials (textures, clothes) that are out there. I'm really not interested in buying everything twice over to support a new figure.