So the major reason to not use this is... that no one does this. Right? I wrote up an implementation of this and it was fairly trivial. The properties all make

So the major reason to not use this is... that no one does this. Right? I wrote up an implementation of this and it was fairly trivial. The properties all make sense - the main change here is swapping poly1305 for blake3. But BLAKE3 promises (and we seem to trust this!) everything Poly1305 does and collision resistance.