Also, in IronPigeon attackers don't get any degree of chosen plaintext or ciphertext except for keys that are one-time use only, so the attack is moot. None of

Also, in IronPigeon attackers don't get any degree of chosen plaintext or ciphertext except for keys that are one-time use only, so the attack is moot. None of the crypto models I've ever read about assume that IV is anything more than nonce quality. In fact in many implementations the IV is given as the first block of a ciphertext (not encrypted itself), so it's hardly treated as a secret, therefore any predictability is harmless.