Don't get me wrong. The general sweep of the argument that "Publius" makes for union under the proposed constitution is valid, even in retrospect, mostly because the colonies would have been unsustainably weak in smaller confederacies, or alone. But the future is always dim, and it's striking how often Hamilton and Madison made projections that turned out wrong in the event. (About thirty papers in, John Jay seems to have fallen silent.)
In a long sequence of editorials, Hamilton argues against limiting the taxation authority of the national government, and the instrument of a tax on income never seems to occur to him; he seems to think that the government of the Union will be able to support itself on import and export duties, and possibly on consumption taxes. I suspect that he would have considered an income tax impractical for mechanical reasons (difficult to administer and to enforce, easy to evade), but would have no objection on moral grounds. He correctly predicts that local government would by financed by property taxes, but misses the level, thinking that they would be levied by the states, not by municipalities as it turned out.
Now Madison has taken the pen to talk about the proposed makeup of Congress. Some critics, apparently, wanted quota representation for each class of individuals, with the exact repertoire of classes left vague. (Madison enumerates, by way of example, manufacturers, artisans, landowners, and merchants, but apparently the critics were subdividing society more finely than that. One gets the distinct impression that they were really being obstructive, trying to make the scheme unworkable by throwing in piled complications.) Madison rejects this kind of apportionment, explaining that he expects the Congress to be dominated by merchants and landowners, and that there will be sufficient motivation for them to faithfully serve the interests of their constituents of all classes. The reasoning is not mere sophistry; Madison's envisioned Congress would probably have been eminently functional. But Madison utterly failed to envision what we wound up with: a caste of professional politicians drawn almost exclusively from the legal profession. I can make a Madisonian argument that this kind of Congress is a bad idea; people who originally made their livings advocating arbitrary positions for money are not the people one really wants to invest with legislative authority. In retrospect the lawyers' monopoly on Congress seems inescapable; it's peculiar that Madison couldn't see it coming.