To the best of my knowledge, his past statments are all scholarly works. The excerpts of law review that he wrote, that I've read, make no claim of "superiority" of sharia over other forms of law, which is the entire premise of the OP.
What The Media Is Not Telling You About The Muslim Who Attacked Donald Trump - Shoebat. This is where I saw the snippets of law review. They do not supprt Shoebat's conclusions either, the excerpts of the law review are clinical dissection of Sharia.
"The invariable and basic rules of Islamic law are only those prescribed in the Shari’ah,” Khan writes. “All other juridical works… must always be subordinated to the Shari’ah.”
Does "all" really mean all there?
He explains that Sharia is derived from the Quran and Sunnah, and that the Quran “is the absolute authority from which springs the very conception of legality and every legal obligation.”
Is he addressing all legal systems, or only Sharia?
It'll probably take a few more days before there has been a fairly thorough review of his past writings and statements.
The key question will be, does he believe the short and simple Islamic concept of law in general: "No man's law above Allah's law." Some columnists think he believes precisely that.