In that same thread someone mentioned OpenFisca [0], which is used to codify tax law. Have you considering utilising it instead of re-inventing the wheel?
It would certainly be interesting to connect the two, but I suspect that you'd do that after finishing US Taxes. Specifically, you could take a completed return from US Taxes and transform it into an input for an OpenFisca model of the USA tax code.
As it stands, nobody has developed a USA model on OpenFisca. Perhaps that could be a next step, pursued in parallel with the US Taxes effort.