Problem 1: battery lifeAny chance they'll release a Magic Keyboard with Touch ID?
Problem 2: security (although you can unlock the Mac with your Apple Watch now, so maybe that's not an issue)
Problem 3: white keys and a black bar don't go well together. Making it a silver background, matching the keyboard case, means the pixels need to be on all the time, which makes problem 1 even worse.
They might be able to solve 1 in time, but I don't know if they'll want to shift to black keys. The could release a separate keyboard with black keys, and keep the "cheaper" white one around too. Wouldn't be surprised by something like that, they seem to enjoy adding more and more stuff to each product line.