If Democrats go back to representing the racist confederate south i agree it could happen. I dont see Dems representing the south again although they will be taking Texas and Georgia soon.
You do realize that for generations after the civil war until the late 1940s throughout the U.S. including the North blacks generally supported the Republican Party over the Democratic Party. To be point where the Republican Party simply took their vote for granted without really delivering on anything helpful to the black community.
The Democratic Party assuming that blacks will automatically support them and taking the black vote for granted is exactly what will lead to the demise of this support over the upcoming decades.