I think most states have some form of inheritance or estate tax, so the foundation is already there. Picketty would argue for a much larger estate tax, I’m sure, but this is, as you allude to, politically untenable. However Texas has an excellent alternative: land value tax. So much wealth is tied up in property. This tax not only targets the wealthy, but disincentivises land banking and property as a primary investment mode. This keeps property prices and rents lower, which is a huge win for the poor in modern Western nations. It’s not a panacea, but I think it’s a viable and proven alternative.