As with any trend, it is hot only until the next thing. These companies wouldn’t have revamped their UI’s without doing some extensive user testing first. Instagram for one tested the black and white UI for months on select users before making the full shift. I believe this trend is beyond the ‘testing it out’ phase. But the question will be what comes after this? If we continue to get even more minimal what does that look like? possibly a removal of User Interfaces altogether as AR begins to take hold?