It is unrealistic to believe that it would always remain so. With the money that was currently being siphoned off by New York going into the Southern economy, other industries would have eventually flowered. Indeed, newspaper accounts of the time immediately following secession detail a massive building boom in Charleston, with every hotel room filled and people leasing rooms in their homes to all the people who came there to take advantage of the new economic situation.
Warehouse space could not be found, and teams of construction workers were hurriedly building more.
They would have eventually ran out of further prospects for more cotton/tobacco production, and would have been forced to invest in other industries or let the money just sit in safes.
The extra money was going to drive investment. Their own ship building industry (Charleston used to build ships.) would have been revived.
The problem that the North East had with the South wasn't that they had slaves, it was that those slaves were no longer working to fill the pockets of powerful people living in the North East. (and Washington.)
Don’t disagree on that point. At some time in the future, the soil would no longer support the volume of cotton production. Other sources of cotton were being developed in India, Egypt and Brazil. These sources would have competed with Southern cotton for the European business. The cotton economy was about a large as it was going to get in 1860. Whether the South would have become a manufacturing power house in a few years, is speculative. Lacking local sources of anthracite, iron ore and other raw material would have slowed the process. Very little inclination for skilled labor to move South because in all skilled trades, the worker had to compete against the slave. Almost every manufacturing operation in the South employed slave labor to some extent. At Tredegar Iron Works in Richmond, slaves made up 50% of the work force. Not only were slaves used for general labor, but they were skilled pattern makers, foundry men, millwrights, machinists etc. Throughout the South, slaves were employed as mason, carpenters, blacksmiths, cart wrights etc. Very difficult for a skilled tradesman to compete against slave labor in those trades. That to may have changed over time, but it would have a long time, IMO.