Doesn't gerrymandering mostly carve out a lot of districts for black congressmen who otherwise wouldn't have districts? I think that's kinda what it boils down to in America. There are conservative areas adjacent to and mixed with majority black areas and they want different representation.
I'm not sure how common it is, but the linked site actually has an interesting discussion of this phenomenon, which Wikipedia calls "affirmative racial gerrymandering"[0], and how it would interact with the proposed scheme: http://scorevoting.net/TheorDistrict.html#Minority
This was more true in the era of overt white supremacy, when majority-white electorates would refuse to vote for black candidates, and thus black candidates could only win elections in strongly majority-black districts. This has changed from the 1990s, which black candidates started winning even in majority-white districts.
However, this also led political marginalization as well. To tilt a purple state Republican, you gerrymander districts so that you have more slightly-Republican districts than strongly-Democratic one. Concentrating black Democratic voters in one district is a strategy both to guarantee the presence of a few black representatives as well as an overall Republican majority.
