Two questions about this:

1. Is it still possible to do a full backup that will let you fully recover from a lost YubiKey?

2. If you set this up and then change your mind and don't want to use it anymore, can you switch back without requiring all of your contacts to go through a rekeying procedure?

Main author here. Sorry for the slow reply, hadn’t realised this had been reposted.

1. Yes 2. Yes

This works because the laptop with a YubiKey will not be the primary device (this should be your smartphone).

So for backup, rollback etc. You just delete Signal on your laptop and relink the device with your primary device.

Disclaimer: the code is PoC quality.