Since converting from Poser to Daz is fairly simple and the other way is more complicated the most common workflow for vendors that support both is to first make a V4/M4 version. Having a finished Poser version means that you have done 95% of the total work. It is neither the modeling nor the rigging that takes the most time, it is the texture. The trickiest bits, bump and displacement can be reused in Daz.

Then you can make 3 packages, one for Poser, one for Daz, and one for both. That which is my own experience was confirmed at a seminar (The best 40 dollar I ever spent) with Xurge I attended recently. Most of the time he spend with the texturing.

Even when Dawn is released I guess it still will be best to start with V4.