Sierra beta won't boot on Late 2010 Macbook Air

I'm seeing it as well. I installed to a USB 3 hard drive, and I'm on a 2015 rMBP. Did you get it to boot yet?

Nope. Reverted back to El Capitan until I hear more or beta 2 is available. 😟

Do you run AVG? Uninstalling AVG fixed it. If not AVG, you might have some other software that has an incompatible kext.

Here is the process I followed:

1. Booted normally
2. Had it crash/reboot
3. Held shift during power on for safe mode.
4. Looked at the crash report, it lists the kexts
5. Uninstalled one package that had a kext
6. Repeated 1-5 until I was able to boot cleanly without safe mode. There were four packages that had kexts, it was the second one I tried, AVG.
7. Reinstalled apps that did not crash the mac.

Thanks! That's a great clue. I'd forgotten to check if AVG was installed on hat old Air. I'll try your procedure as soon as I get a chance. I suspect you nailed it!