These ideas are pretty close to discredited in cryptography engineering. Diversity in signature algorithms doesn't help when everyone uses the same algorithm anyways, and, more importantly, a negotiated algorithm makes it harder to recover from an new attack on algorithms, not easier: with a non-negotiable algorithm, you version the entire repository, and can reliably rule out vulnerable signatures. Negotiation and downgrade attacks have been endemic in "ciphersuite" schemes.

There's a reason the field is moving towards simple, modern schemes like this one, and Debian has more experience than most in trying to make broken, crufty old PGP work.