Yes it is and so was probation but it was over turned (now we can drink :-)) and the “Fair Tax” can abolish the 16th Amendment (without the Prebate!!)
Your point about “I'd go with axing the agencies that aren't explicitly-named or implicitly-commissioned in the Constitution” is 100% correct and would help make our Government a lot smaller.
Prebate is a stupid idea and, if we're fair with ourselves, so is the fair-tax: it involves the FedGov in all sales. (Sure we could manage things easily, maybe a smart-chip in the hand or head…)
I'd actually rather an income tax, and a flat-rate, with no exemptions no write-offs, no credits, no rebates, and no withholding.