AFAIK only Samsung used a fingerprint scanner on screen and they've already ditched that... But yeah, I kind of get your point 
You mean on the Galaxy S5? That would have to be weighed in regarding data randomness obtained in both methods and if the security given by one method tops over the cost saving the other method offers.
I'd say generally, that the retina scan should provide better security however there are obviously important factors that play a role in this. I wonder how secure the iris scanner in the latest Galaxy Note is.Since it would only be to recover a passphrase, I'm not sure if it would be all that impractical (you would only use it once in a while). We would probably have to build hardware for that tho... Lips are very distinct, and they're also used for investigation in forensics, hence my idea 
Indeed. It is less impractical if rarely used, although I do wonder the implications of this. From what I've gathered, there's only some research in this area.Correct, it's the S5 that still had in on screen.
I assume the Galaxy Note uses a Secure Enclave-like system and encrypts keys on a separate chip
Furthermore, there are 2^160 bitcoin addresses, 2^63 grains of sand on all the beaches on the Earth, and only 2^33 people on this planet. Using a fingerprint, just like using a brainwallet, significantly reduces the set of possible keys and therefore decreases security. Given that vanitygen on a GTX970 can do 40Mkeys/sec, it would take just over 3 minutes to calculate 8 billion keys; this means your fingerprint based brainwallet will probably be cracked pretty damn fast.
This is something I'm really curious about... What about retina/iris, would it increase the set of possible keys?