Anecdotal evidence here but I've overheard some people in shops asking for a black version and seem quite persistent, customer service people said there was a black/grey one coming but it's 400 quid which ends the conversation. Also some of my friends say they would buy one if it came in black and don't really like the white or white controller, the X has them interested because it's not white would you believe but the price soon brings them back down to earth, Sea of Thieves seems right up their alley as another little tidbit and still in for Halo 6 if it's more like the old games. So, Microsoft release a matte black Xbox One S and make a good Halo so I can play with my buddies, fixing Halo MCC would also make it happen faster!
Here is a picture to give you an idea.
The Limited BF1 grey version.
Maybe Microsoft made a billion white versions to get through, the FIFA bundle never ends.