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Dawn is working with the dynamic that DAZ has already set in place. That dynamic wasn't there when Genesis for appeared, and like I said, Studio was already converting clothng with auto-fit, a feature Poser didn't have.  So continuing to make the clothing Poser compatible at least until DSON came along would have ameliorated the splt somewhat.

Not really because in reality Poser and DAZ came out with different weightmapping systems and at genesis' release Poser didn't have the scaling fixed and no subdivision. Scaling didn't get worked on until a service release and subdivision didn't come out until Poser 10/2014 (though edge weighted creasing from Pixar's spec needs to be added in). So really even if genesis didn't get released, any future figure couldn't be released in both. The split was going to happen regardless because both companies aren't on the same page feature-wise and those features aren't compatible.

So let's take Genesis totally out of the equation and just look at the apps themselves.

Future figures would be available in only one app or they would to be "Dawns"... figures with base features that would exist in both applications. Vendors would just make stuff for one application or doing it twice for both; things made in one program would be met with cries from customers to see if they can get a compatible version for their application. But really the burden falls to vendor to make stuff for both applications, which they won't do for too  long. So those vendors that didn't want to split the market would stay with the older tech until the customers start wanting something different and gravitate to whatever software gives them what they want, then those vendors eventually will have to choose.

But SM provided the plugin architecture and DAZ created the DSON importer to allow genesis to be used in Poser. So it's a not a perfect solution, but at least the figure can be used in both and vendors don't have to duplicate their efforts to get something to the marketplace. And that's what vendors want: to be able to reach the most customers without increasing their effort.