Dumander, I would tend to agree with your take that the comma after "equity" is significant, for grammatical reasons of which the framers would have been well aware. The framers could have chosen a different construction of the sentence altogether if they did not intend to say that the judicial powers of U.S. shall not be construed to any suit in law or equity, period. The judicial power at the federal level was only vaguely defined in the Constitution at any rate. The framers perhaps envisioned most litigation being confined to the local and/or state level. The states being foreign nations with respect to each other, it makes sense to me that the judicial power of the U.S would be properly confined to an admiralty jurisdiction. This would be a limitation on judicial power favored by opponents of a strong judiciary, i.e. anti-Federalists.

The First Judiciary Act would seem to contradict such an interpretation, as it provided for suits in law and equity. However, it is always possible for laws that are passed by Congress to be unconstitutional. The Act passed in the Senate by a vote of 14 to 6. The Act was opposed strongly by Senator William Maclay as a "vile law system, calculated for expense and with a design to draw by degrees all law business into the Federal Courts."

Nowadays, all Federal Courts operate in admiralty anyway, so it would appear to be of historical interest only IMHO.