The 12-inch Macbook has an F-key row which is what gets replaced with the touch bar.
I only estimated that they were going for 100% laptop coverage. But I can imagine a future where Apple keyboards have a touch bar option. Though not as important because Macbook touch bar penetration can drive developers to integrate with it, alone.
At which point it's not much different than gestures when it comes to answering your questions. What happens when you use a Logitech mouse on your macOS desktop instead of a Magic Trackpad?
Note that touch bar integration cannot have unique features, so it's never required. The challenge is to get developers to care about it which is the prerequisite for users to care about it.
I only estimated that they were going for 100% laptop coverage. But I can imagine a future where Apple keyboards have a touch bar option. Though not as important because Macbook touch bar penetration can drive developers to integrate with it, alone.
At which point it's not much different than gestures when it comes to answering your questions. What happens when you use a Logitech mouse on your macOS desktop instead of a Magic Trackpad?
Note that touch bar integration cannot have unique features, so it's never required. The challenge is to get developers to care about it which is the prerequisite for users to care about it.