Quote - a long time ago now, i had an idea for a skull cap with preset hair growth zones on it, eg, fringe, front side L, front side R, side R, side L, top, back etc etc, essentially a predivided skull cap , the idea being you could just select the hair zone in the hair room and grow you guide hairs, anyone thing there would be a demand for a prop like this, and what do you see the problems that may arise ?

I would LOVE something like that. 

A big problem with the skullcaps currently available is that they are way too high-res to be ideal in the hair room.  Dynamic hair collisions only work well if the objects involved are relatively low-resolution.  Poser just can't handle it otherwise. 

Many skullcaps have thousands of polys.  The Poser 6 skullcaps cut that drastically, down to about 200 polys (about the tenth the number in the Poser 5 skullcaps, IIRC).  Today's technology would probably allow a bit more than that, but still...low-res is where it's at, for dynamic hair.

Having different growth zones would be great, because then you could have higher resolution (and hence higher hair density) where it mattered.  Along the hairline, for example, where you can actually see the strands.  You could also run in a sim on only one or two hair groups (if you're animating).  That would be enough to make it look like the hair is moving like real hair, but reduces the resource load, and would also let you preserve the styling in the other groups.

A couple of tricks that Kirwyn, now not around much, used for his Genesis Hair (before DAZ co-opted the name ;-).  He modeled the skullcaps tilted back 30 degrees, so that the hair would naturally fall back a little, instead of into the figure's face. 

And he designed the skullcaps so they fit just inside the figure's head.  With the skullcap inside in the head, the hair appears to be growing naturally out of the scalp.  (Poser ignores the first part of a hair strand when doing simulation calculations.)

That means you can't texture the skullcap to cover bald spots, but you could add another, visible skullcap later.  (I use 3Dream's universal skullcaps.)