The fact that we don't have a good method makes it a problem. The only implementation of cards to seed phrase I am aware of is Ian Coleman's, which as we have already discussed here is not great. I am not aware of any other implementation, and I'm certainly not going to propose one. They obviously can't be used "as is" since a seed phrase or a private key needs to be presented in bits, and a string of cards is not in bits nor directly convertible to bits without applying some kind of transformation.

This gets us back to the original discussion regarding converting a string of dice rolls in to a string of bits, which as I argued before, should not just be a case of applying a hash function and assuming you now have a cryptographically secure random number and you are perfectly safe.

So again, I would say that if you don't trust /dev/urandom for some reason, then stick to flipping a coin to produce a string of bits directly. Anything else is more complicated, more time consuming, and potentially less secure.