While I am a strong proponent of a Flat Tax over the FairTax (because of the price inflation noted on page 144 of "The Truth", caused by embedded taxes in gross salaries), I am an even stronger proponent of the prebate as a way to make either tax far more progressive.
However, I don't think your prebate goes far enough. My 10-25 Plan takes the funds from tax deductions ($1T) and means-testing programs ($700B) and 1/3 of Entitlements ($400B) to make a true safety-net that brings every citizen up to the poverty level and saves the country $500B per year. It also promotes personal responsibility over dependency and gets rid the 700,000 bureaucrats that run the means-testing programs.
Nedland P Williams, Author of "Fixing Everything"