Neither plausable, or feasible. The economy would crash instantly.
Not according to the sources that RobFromGa is quoting, in fact that source, Jorgenson, claims as much as a 10-13% increase in real GDP with replacing federal income taxes with retail sales taxes in just the first year, with sustained growth well above what is achievable with current income/payroll tax law going forward.
What you are neglecting to perceive is that the economy is no more burdened with federal tax than it is today under the income tax syste and the the advantages to the economy arises from increased production efficiencies, lower production costs, and increased investment and savings driving further gains going forward. Of significant mention is the the opening up of additional potential for exports by making our own products more competitive in foreign markets while assuring that foreign goods do not receive favorable tax treatment over domestic production as happens in today's economy under the income/payroll tax system.
Jorgenson also assumed that everyone would get a big pay cut, which ain't gonna happen. All the analysis you are relying on needs to be thrown out because the inputs are faulty.