I think one point not mentioned would be for it to be marketed in the Daz store, as well as work well in DS (unfortunately, the divergence on weight-maps makes this problematic)

Like it or not, Daz is where most "beginners" go, for the free software.  It's where I started.  Beginners (and there is always a steady stream of them) also spend a nice little clump of change when starting.  This money means vendor support.

Figure-wise, other than maybe Cookie, are there any non-Daz marketed figures that have done really well for vendors (not counting Posette)?

Does Daz allow non-Daz human figures?