I went through this in a previous post. See Considerations for Network-level Validator Privacy in Proof of Stake.
To reiterate, onion routing, although doesn’t offer resistance against a global passive adversary, is the best option given ETH2.0’s goals. That being said, I wouldn’t completely recommend vanilla onion routing protocols that we see deployed in the real world as there’s current research that improve upon those designs. The main issue is these designs haven’t been deployed widespread in production (some may not even have research implementations!). There’s still work to be done to make something that is best suited for ETH2.0.