"Revolutionary government" is the ultimate hidden target of Duterte and his legal and security teams. Not martial law.
The Constitution constricts the martial law powers of the Executive in reaction to the dark, violent, corrupt and hypocritical regime of The Dictator Marcos.
Duterte wants a totally unhampered one-man rule. Only a revolutionary government can give him that satisfaction.
His lame excuses -- war on drugs, ISIS, Abu Sayyaf, and others that he might soon invent -- do not constitute invasion and rebellion, the two limited grounds allowed by the Constitution to declare martial law.
What Duterte really wants is a revolution and coup d'etat from the Center/Executive, the very same philosophy that Marcos peddled to the people in the 1970s to justify his dictatorship.
This time, though, Duterte is unsure as to whether the Military and the Sovereign Filipino People would obey him and as to whether America and world opinion would support his move.
He bids his time.
Meanwhile, he conditions the minds of the people by his outrageous threats, by the fake news of his his social media trolls and spin doctors, and by promoting sensationalized police operations against criminals --- the same old tactics of Marcos and Hitler.
Duterte is Marcos and Hitler reborn.
To him, the Democratic System is a necessary evil within which he is constrained to work.
He is fed up with Democracy.