Massive changes, although slavery is certainly not going away here as speculated upon.
@David T has pointed it out before that as late as 1800 only about 11 percent of all slaves lived on cotton plantations while concurrent to this about as many Africans were brought into the United States (from 1780 to 1810) as during the previous 160 years. This is explained by the fact that alternatives to cotton existed, such as tobacco still being profitable in Virginia and Maryland, while rice was likewise in the South Carolina lowlands. The aforementioned tobacco was also growing in importance, as cultivation had spread into new regions such as South Carolina, Georgia, Kentucky, and Tennessee. Slaves were also used in the production of rice, sugar and grains; that last one in particular is major, as the South produced more corn than the North as late as 1860 and the value of that exceeded the value of the cotton crop:
However, I think you're very much right on a more industrialized South.
Industrial Slavery in the Old South by Robert S. Starobin showed that slavery was more extensively used in industrial or proto-industrial processes than commonly known, and was at least just as efficient as free labor sources available in the South while also being cheaper. He also found that industrial work involving slaves contained a high rate of return, sometimes rivaling cotton, so I'd imagine in this ATL that many planters would take to getting into the manufacturing business as the Industrial Revolution gets underway. Birmingham in Alabama, among many other cities, will definitely get developed sooner as
@Jared has pointed out nearly occurred anyway before.
Finally, and ironically enough, this may actually serve to make Slavery
more powerful in the United States politically. To once again cite David T:
Oddly enough, a delayed invention of the cotton gin might actually have led to more slave states, as I once noted in soc.history.what-if:
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Robert McColley in *Slavery and Jeffersonian Virginia* (Urbana: University of
Illinois Press 1964) argued that the cotton gin, far from giving slavery "a
new lease on life" (as is so often claimed) may have sealed its doom by
making it so profitable in the Southwest that there was less pressure to
introduce it into the Northwest.
Yes, such pressure could exist despite the Northwest Ordinance. Even in
OTL there was considerable evasion of the Ordinance, and petitions by some
people in the Illinois and Indiana Territories for at least a partial
repeal of its antislavery provisions (one of them was supported
by Indiana Territorial Governor William H. Harrison, a future President
of the United States). And presumably the Ordinance could not prevent
states from adopting slavery *after* they were admitted to the Union [1]
as Illinois seriously considered doing in OTL in the 1820's. With more
southerners moving to the Northwest (because of the lack of an early
cotton boom in the Southwest) the already considerable pro-slavery feeling
in early Illinois and Indiana could be a lot stronger.