On page 37 of this analysis, Halliwell says:
"...It is...the primary purpose of the Poetics to establish a philosophical framework for the understanding of poetry in general, and to do so in a way which entails the statement and advocacy of criteria of poetic excellence. The treatise is in this sense both theoretical and prescriptive. But it has sometimes been believed that it is also prescriptive in a stronger and more pragmatic sense: that it sets out to instruct poets or would-be poets in the methods of composition itself."
I wonder if the Natyashastra and rasa theory as analyzed by Abhinavagupta is somewhat the same. Most historians agree that the Natyashastra was NOT prescriptive but rather described the arts as it was performed when it was written. (Theorized to be 500 BC to 500 AD, if I recollect properly). However, I think it is extremely difficult to analyze such methodology in detail without ultimately becoming also prescriptive.
The Natyashastra nowadays is definitely a prescriptive text. But if you think about it, it is comparable to a book like Aristotle's Poetics. Which allows for more leeway than one would think - it is now a text actually written by someone, who, for all intents and purposes, can't be right about everything. Is there anyone out there who would analyze, and above all, challenge the Natyashastra?