Never. If the day comes that black votes outnumber white ones, then it won't be competitive. It'll be a consistently Democratic state even if the margins aren't exactly great.
Despite our revisionist histories and obsession with realignment theory, contemporaries largely saw the South as a swing region, if not THE swing region, for much of the period between the mid-1960s and ~2000. It’s only with our 20/20, post-2000 Election hindsight goggles that we envision a Democratic Solid South fleeing to the arms of the GOP and never looking back.
There are plenty of interesting articles I’ve seen from throughout this period talking about how Democrats likely couldn’t win states like Alabama because of the combination of suburban voters being solidly GOP (as they were in most of the South), the stridently conservative Gulf Shores area AND a perceived racial divide that was driving Whites into the GOP at a faster rate but how states like Georgia or Arkansas COULD be competitive because the aforementioned trends and dynamics could be counteracted with combining Black support with enough working class voters that “didn’t have the privilege” of voting on racial lines and would favor Democrats on an economic perspective.
It’s never talked about because we like to simplify things, but pre-2004 “Jesusland Map,” there actually was often a perspective that Southern voters who prioritized “racial issues” and therefore voted Republican were your anti-busing types in suburban areas rather than our current caricature of a racist rural Trumper. This naturally (and insidiously, if you ask me) changed as Democrats began losing more and more support from the rural South and gained more in suburban areas. As late as 2008, you had NYT columnists (can’t remember if it was Nate Silver but someone of a similar profession) outlining Congressional and gubernatorial Democrats’ path to victory in Southern states as dependent on White rural voters, white urban voters and Black voters, with emphasis on the first believe it or not.
