If I prototype something with an Arduino, I can easily switch to directly sourcing ATmegas and spin my own boards.

The Pi Zero is the next thing over from vaporware. I know some people who have a few, but all of the official vendors linked from https://www.raspberrypi.org/products/pi-zero/ are either out of stock, or have "limit one per household."

I'd been having trouble figuring out where to source the BCM 2835 SoC that powers the Zero, and there's (allegedly) a reason for that: https://olimex.wordpress.com/2014/08/28/who-fears-from-the-c...