I wrote up in the TLS mailing list why I think composite signatures (ML-DSA + ECDSA/RSA) are a net negative, will hurt the ecosystem, and should not be implemented. Hybrid key exchange was simple and self-contained. Hybrid signatures would be a mountain of complexity in code responsible for half of sev:crit in crypto libraries since 2020. https://mailarchive.ietf.org/arch/msg/tls/oh3jmmkHzHdp1hk4R4M9QjkmvBk/