Boot Camp has already been addressed though. The function keys will be shown and since Touch Bar is running WatchOS it should be easily possible to show them without drivers.
I read that there is an independent ARM processor controlling TouchBar. Is there solid proof the TouchBar reverts to Func keys when no OS has initialized/rendered keys to the TouchBar?
I was looking at that article as well. I read that as confirming how the Touch Bar will work under Windows in Boot Camp. GP is asking a different question: how will the Touch Bar work for non-Windows OSes, in particular during the boot or OS initialization process itself?