> “Doesn’t the NSA lie to break our encryption?” No, the NSA has never intentionally jeopardized US national security with a non-NOBUS backdoor, and there is no way for ML-KEM and ML-DSA to hide a NOBUS backdoor.

The most concrete issue for me, as highlighted by djb, is that when the NSA insists against hybrids, vendors like telecommunications companies will handwrite poor implementations of ML-KEM to save memory/CPU time etc. for their constrained hardware that will have stacks of timing side channels for the NSA to break. Meanwhile X25519 has standard implementations that don't have such issues already deployed, which the NSA presumably cannot break (without spending $millions per key with a hypothetical quantum attack, a lot more expensive than side channels).