I am sure people could adjust to this. I am not certain how many people actually use those buttons without looking at the keyboard anyway. When I learned to type the function keys weren't included, I for one, always have to look when use a function key, and generally have to look when typing numbers too.
If you're constantly using one or two function keys, it's fairly common to do it by memory. For example I can hit the volume and brightness buttons and f5 without looking. But really, all the other functions that will become available with the touch bar will more than make up for the time lost looking down.
