I don't REMEMBER being discussed before, and it sure would make a difference.
If it happened early enough, you might find that the importation of slaves is NOT outlawed in ?1808?, and that, in any case, slavery digs in much faster and stronger than OTL. The southern states will be (even) richer and stronger than OTL, which may be a problem considering how much the Virginian Dynasty was resented in other places.