There could be ways around that...
Eliminate the Income tax but retain the Alternative Minimum Tax in some simplified form. Then give a Sales tax credit that will offset the AMT (This would however, require that taxpayers maintain receipts from transactions on which they pay the federal sales & Use Tax.
I think you might see this happen with internet sales at some point in the future if we elect a President who would not veto such legislation...that could then be a first step to setting up a more encompassing federal sales tax system.
Scott