I think the OP was more in the tune of 'picking the right horse' to bet on becoming mainstream and creating content for it, rather than probing for thoughts on what to put into an upcoming figure.. though I dont want to put words in anyones mouth.

For my 2 cents... content is as big a factor as anything in making a figure 'mainstream'

BH gave alyson a huge boost just by releasing anastasia, granted the rest of the content is still lacking but without anastasia very few people would even want more content for Alyson 2.  If another vendor with a significant following (say alfa seed/Aery Soul .. just for example) were to commit to support that figure it would quickly start to become at least one of the mainstream figures.  

The unfortunate reality is that it matters significantly less what quality is in the figure than it matters what quantity and quality of slutwear* that is available for her

*no offense to anyone, some of the slutwear on the market is very artfully and skillfully crafted

Quote - I have two thoughts.

1.  It needs to be something anyone can use.  If you have a  dragon figure that everyone would want at the price they want, it'll be mainstream.

2.  Why does it need to be mainstream?  If you do it as a labor of love or something that you want and you manage a little money back from it, that should be a good thing.  I haven't modeled in almost a year, but when I was, I was making things I wanted or needed first and foremost.  I think that should be goal one.

If you try to make mainstream for the point of being mainstream, you'll probably fail in some respect because your initial focus is wrong.