Hello,
I've written a short gist demonstrating how to enable bluetooth functionality on the Pi Zero W
(and possibly Pi 3 B) after the new configuration changes to the kernel.
https://gist.github.com/shenghaoyang/92e6dd65b9f0cc736a419f3e640663c2
Hopefully this can be of help to those using btattach or hciattach for their bluetooth needs.