Are mainstream symmetric cryptographic algorithms practical in Cairo?

[copumpkin]

I believe the ZKCP pay-to-sudoku demo assembled a symmetric stream cipher from a hash function, but I'm wondering whether the advances in Cairo have made it possible to implement more "mainstream" symmetric encryption algorithms nowadays?

Has someone already done this? If not, is it worthwhile trying to implement a standardized cryptographic algorithm in Cairo, or would the proofs still get impractically large at this point? Or are there other barriers that would make it unpleasant right now?