Remote unlocking won't help people whose devices are stolen either. Worse, recyclers would have very little incentive to help because they paid for the device.

> What would be the "backdoor" of allowing recyclers to prompt users to remotely unlock or authorize apple to issue a signed unlocking code for that particular device?

You'd need to store the encryption key somewhere and make it available for remote use. This is scary enough IMHO.

> it seems like many recyclers and refurbishers do attempt to educate users that devices should be unlocked.

This is not about user education. Recyclers should not accept locked devices in the first place.