I was thinking the smart contract part would just be the periodic disbursement of funds, nothing complex. The hope was that using a cryptocurrency and smart contract would make periodic disbursement untamperable. If smart contracts can be tampered with, then I see no point in their existence. The untamperability of a disbursement process for cryptocurrency would depend on the implementation. Maybe it's not possible to do that. Has anyone tried? Maybe the money could always be shut off at the source, but that could also take down all payments (something the Democrats are currently threatening to do). Bugs in such a system could be a big problem, they might initiate things that would be very difficult to stop. Ultimately the input to the system, the laws passed by Congress, would affect the correctness of the system. Laws are not always logical, which could be an issue, though they tend to get very specific where money is involved.