All the people I've seen playing it don't seem to show any specific way to do mixed use, so if it does exist it's probably just a thing that happens automatically on high density housing units
It gets unlocked later and the embargoes were staggered so they couldn't show certain milestones in the game. The newer videos will have it now, so look at those to see everything, including how their computers are chugging even with brand new hardware on high settings.