Will the librem 5 be able to optionally boot from an external storage (SD card / USB OTG drive)? This could open interesting possibilities, such as using a backup copy of the OS in case of problems, or using live distros such as Tails.
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this is an interesting topic. how is the device booting anyway? can it be bricked? how can it be recovered? how is it protected against thief or evil maid?
It’s specified to use a free software bootloader.
To me that implies that it will probably be running U-Boot, or something similar. U-Boot supports booting from external storage media, though it can be built without that facility, so it’s down to Puri.sm to decide.
So, I would hazard a guess that this is something that the hardware will be physically capable of, and which should be achievable with some poking around and maybe reflashing, but it might not be exposed as a feature out of the box.
As for evil maids, apparently the i.MX processors have a “High Assurance Boot” (HAB) feature, which could presumably be used to protect against evil maid attacks. I found this article about HAB.
I only just read that HAB exists, so I don’t know how free it is in terms of enabling users to sign their own software. I wouldn’t be surprised if setting the allowable public keys is a one-time operation that permanently burns them into ROM. Clearly you can’t have a Free Software phone that only runs binaries signed by a single entity. It would need some sort of mechanism for the end user to securely control what public keys it uses.
Please Purism allow changing of boot order AND boot from microSD so I can tell my L5 to search for bootable media first at the microSD port 
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