What if instead of one Third Entity, there are three? So five total, including ECC and ZF. Require 4-of-5 multisig, and suddenly it’s much harder to capture the decision-making process.
It might be ideal to have three entities focused on Zcash, and two from the larger ecosystem.
Keep and Summa’s Cross-Chain Working Group might be a good candidate: Summa and Keep Partner on Cross-Chain Working Group | by Laura Wallendal | Keep Network
The Tezos Foundation also comes to mind.