Oh I have no idea if this is possible or even practical, I just was looking at my boarding passes and thought they were boring.

Phone readable QR codes require "eyes" for the phone to align and register. In a square QR code, the eyes are in the corners, but they could be anywhere and a custom shaped QR code is just a square QR code with random QR looking patterns surrounding the square. The SWA boarding pass QR doesn't appear to be readable by phone, I'm guessing it uses a different protocol. Everything I know about QR codes I learned from qrcodechimp.com.