Apart from the obvious kph advantage the F-Duct offered or the 2nd brake pedal, there are not too many things to copy that lead to a giant gain in performance, are there? Even the cracks of this forum only have a vague understanding of why the RedBull was so quick the last two seasons (use of ellipses etc.
So if RedBull gave it the full beans now, how would another team be able to spot THAT detail making RedBull fast? To my understanding it is the whole package, lots of excellent solutions working together very well. So the only chance would be copying the whole car.
It may be that the one or the other car looks fundamentally different come Melbourne, but that would even more be a reason not to hold back your performance because whatever the other teams see and copy, is not what will on the final car.