Struggling to see the benefit of the enclave managing the group members instead of just an admin, but maybe I'm just missing a bunch of details.

For the decentralized enclaves, I've been doing this exact thing using TLS established with quote attestation so that you're doing only trusted comms. Once Intel shutdown the CAS servers and discontinued consumer CPUs with SGX it became a huge PITA lol.

Another thing I've worked on was using distributed (or threshhold) signing of the enclave so that a party can, as you said, collectively agree on a new enclave.