To answer the original question, just look at the history of DAZ figures:
 
V3 wouldn't take V2 stuff unless you used the V3-V2 figure, but that figure didn't take V3 or V2 morphs.
From what I've heard, the V4-V3 figure will be the same: it will take V3 stuff, but it won't take the morphs of V4 or V3.
 
Sure, PhilC will be providing Wardobe Wizard support, but realistically, how many people use that program? How many people will be clamoring for all-new clothing specifically made for V4?
 
In other words, like all of the V2 stuff, all of the V3 stuff will soon be obsolete.

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