I'd say that Democrats have 4 tiers of winning:
Tier 1: Currently winnable, or maybe in 5-10 years
Virginia is already Safe D
Texas
Georgia
Florida
North Carolina
Tier 2: Will become winnable if demographics trend properly in around 15-20 years
South Carolina (Greenville/Spartanburg slowly trending D)
Mississippi (becoming slightly blacker)
Tier 3: Too far off, but could become Tier 2 states in about 25 years
Alabama (Birmingham, Huntsville, Mobile all have potential to become bigger metros)
Louisiana (NOLA, Shreveport, and Baton Rouge put together with enough D suburbs)
Oklahoma (Most rural areas are losing population and OKC/Tulsa are trending D)
Tier 4: Not in the foreseeable future, barring a realignment or Roy Moore scenario
West Virginia (no path here, already Dems are running on fumes)
Kentucky (too rural and white , and Louisville and Lexington aren't big enough on their own)
Arkansas (see Kentucky)
Tennessee (see Kentucky)
Well Nashville and Memphis are bigger than any city in Alabama or whatever by far. Why do you think Alabama could go Dem at some point in the future but not Tennessee?
Yeah the characterization of Tennessee is way off.
Yes, and even Kentucky has greater prospects for trending left than Alabama (not that any of those states should be competitive remotely soon).