What would happen if Shays rebellions succeeded in its mission and marched on Philadelphia
I think the government would not be all that powerful. When Washington kicked Shays ass the entire US shat a collective brick and decide to not push the governments buttons. If Washington was defeated their would be more rebellions and possibly, if all goes wrong, separate states.
You mean Boston. Why would they march on Philadelphia?
They would have set up a more broadly democratic state government in Massachusetts, similar to the one in Pennsylvania. They would have begun paper money emissions similar to the ones in other states to ease the burdens of debtors. They may or may not have adopted something like the direct election of judges or perhaps even something more radical related to the judicial system.
In the long run the ramifications would have been enormous. A kinship social system would have successfully defeated and toppled a state-capitalist social system and one of the less democratic state governments would have been replaced by one of the most democratic governments. New York's state government, especially, would have started shaking in its boots. The Constitutionalist party in Pennsylvania would have seen a huge boost as they were joined by another radically democratic state government.
I can imagine there would be unofficial condemnation of what happened from some of the more securely limited franchise states and other butterflies in the other states, but I'm not exactly sure what they would all be. Similarly, there would be deep social implications as time goes on throughout the early United States. Popular power, which was already at a high ebb IOTL in this period, would drift even higher.
There isn't going to be a Federal Constitution ITTL, at least nothing like what happened IOTL. Even if something like the Annapolis and Philadelphia Conventions happened, if pro-Ratificationists tried to pull in a democratic Massachusetts what they pulled in Pennsylvania, only a few years after armed resistance had ousted an unpopular government in MA, many people will just not accept it and will call alternative ratification conventions and reject the draft constitution.
If the federal government is in any way strengthened over the federal government of the Articles, it will be significantly weaker than that of OTL and might even take several rounds of drafting conventions and rejection by the states before it is adopted.
It wouldn't necessarily be any more directly democratic, it would just include a broader franchise earlier, as well as probably having similar institutions to the radical Pennsylvania Constitution of 1776. That is, a unicameral legislature, a weak executive with little capacity to over-rule the legislature, and other institutions of the radical wing of American politics in the North in this time period.
I agree, but I doubt the staying power of the rebellion's government. At the end of the day, the farmers were to back to their fields and families and the political class will come back of their holes to seek retribution.
The reality that Shay's Rebellion was not a broad popular movement throughout the state, much more localized. Furthermore the economic policies they advocated were completely disasterous, and could not be maintained...
Well, A successful Shays' rebellion is not doable long term.
However let's just say that they manage to take Boston. They burn all the land and debt documents held by the courts, the government, and the banks. Such an event I think would spark one or both of two reactions, one potential, one guaranteed. The potential reaction is that it inspires similar rebellions across other states where similar preceding events occurred. The guaranteed reaction is that an army is called up to take Shays down.
If the successful taking of Boston does not inspire similar uprising across New England, it will lead to the congress calling up an army, and possibly calling up Washington out of retirement, to crush the rebellion. If this happens than we see the creation of a constitution with more authority vested in the Federal Government, and we probably don't see the restriction on the Federal government sending in troops into a state without that state's permission, along with a few other things.
However if the taking of Boston does inspire similar uprising across New England and possibly the rest of the United States, it will definitely call Washington out of retirement and put together an army. They would most likely try to take Boston back first and then hang Shay and the other leaders to make examples of them. They do this in hopes of scaring the other rebels in other states back to their farms so they don't have to fight more. This also leads to a constitution being formed with a much stronger national government, with little authority being granted to states. We might even see a model Hamilton proposed being adopted out of fear of too much popular democracy.