If it happens, I would think the test case would come out of inland California in the 2031 or maybe even the 2021 round of redistricting, not some hypothetical mid 21st century Mississippi. However, SCOTUS appears to be inches away from ruling that the VRA doesn't apply to redistricting as it is, and one more Republican appointee would almost assure that.
Except whites in California are very Dem-leaning, unless you're suggesting either they will become majority Republican or California becomes majority Republican.
Locally, in the eastern CA districts they are quite Republican.
