Most nations already have a progressive income tax (higher tax rates for higher marginal incomes). Adding basic income on top is effectively what you propose, b

Most nations already have a progressive income tax (higher tax rates for higher marginal incomes). Adding basic income on top is effectively what you propose, but much simpler (cheaper) to implement. It's certainly true that the basic income needs to change over time, but it should probably increase at the rate of inflation, rather than at the rate of the GDP. I suppose the latter might have some advantages, though, as long as a depression doesn't reduce the basic income, which would be completely counter-productive.