The issue with Genesis 3+ is the dual quaternion skin-bidning, not the use of a single weight map (which a triAx-only setup could mimic by making each map the same, and zeroing the bulge maps).

Duf was a move to an open standard (JSON, as you say) rather than the proprietary, binary .daz format. The initial releases of DS 4 beta could, as I recall, save to .daz (I'm not certain of the sequence there) but I don't hink the chnage in formnat was forced - the old format already had the ability to handle weight-mapped figuers, as fdar as I know (the OptiTex clothes) and could certainly handle separate morph files so it could quite plausibly have been extended as needed (but the format was becoming problematic regardless).

Giving Poser the ability to import .duf content would not require copying the content, so I don't see how it would entail copyright concerns. Poser now has many of the required features, Dual Quaternions being an obvious exception, but of course that says nothing to its practicality or desirability, and of course an imported figure would not have built-in support for soem Poser antive featrues such as Walk Designer.