The issue parses into several factors.
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The absence of the promised but as-yet unreleased SDK, which is most likely the missing component to more powerful and innovative user-created plugins.
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Incomplete information about the functionality of the existing ZScript command set including the use of external calls.
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An understandable reluctance by Pixologic to commit resources to supporting the ZScripting community at the expense of essential development efforts on the next version of ZBrush (and, I suspect, undisclosed future Pixologic projects).
The current success of the user/scriptor community is the product of enthusiastic and dedicated individuals and their willingness to voluntarily share information about ZScript’s basic functionality and its more obscure and undocumented features.
I for one learned what little I know about ZScripting from reading the early source scripts posted by Pixolator, himself, and other members of the pixologic team and other .txt scripts posted by the user/scriptor community. I also learned a lot through patient detective work in reading ZScripts that I recorded myself along with seemingly endless hours of trial and error.
I’d be interested to hear what other ZScriptors have to say on the subject. 
Sven
