Stealth addresses can be complementary and useful but I don’t see it having the same properties. If following ERC-5564 as intended, then you still see the full flow of transactions. A mixer or shielded pool has to eventually be used to break the link from sender. In the shielded pool example I shared however, nothing would be revealed at all. Not sender, recipient, nor amount.
Now if data is not in object but one can bundle transactions here, then yes true compromises can be made to achieve some level of parity. For the shielded pool example, you could technically emit an event log that includes the additional data. The problem with that though is it becomes much costlier and complicated to prove client-side in a zkSNARK. Another option to avoid that is instead hash that data as a commitment and insert into a separate merkle tree in a smart contract. Then in the zkSNARK, I am proving the inclusion of both UTXO note and its corresponding commitment in their respective trees. That’s quite fast and cheap to do client-side but tradeoff would be high gas cost of each commitment inserted into the separate merkle tree. There are ways to make it more gas efficient but still unideal. Compared to both of those options, just having data in the UTXO object would be much simpler and cost-efficient.
To counterpoint my escrow example, that also can be bundled with a transaction to some smart contract that maps UTXO note to an unlocked_at timestamp and then later escrow address can check it as a verify frame and release funds as new UTXO note to recipient. I don’t know if there’s anything to gain from using native UTXOs for that specific use-case, even if its a sort of private escrow, if it has to update state in another smart contract. I’ll admit though, the escrow example was only to prove multiple use-cases open up with data included. I think there can be many more.
Also, I don’t think a verifier would need to be enshrined for this. From my understanding of EIP-8141, you can verify an zk proof in a frame. If that is false, then it would be an incredible bummer.