In this case, I would suggest dropping income tax altogether, decommissioning the IRS, and using the state infrastructure already in place to collect an equal amount of revenue from sales tax.
No filing. Broader tax base, including criminals and illegal activity. Everyone's checking account effectively becomes a 401k.
Sales tax is regressive, yes. But proposals like the FairTax suggest the idea of an annual "prebate" or credit up front in the form of a check that effectively eliminates taxes on spending up to poverty level income.