It's also not that useful, as payments can trivially be denied by a fraudulent receiver, with no recourse for the buyer.
Payment proofs are a critical component to a functioning digital payment economy.
Requirement that both agree to release it is what enables fraud. If I pay you X in exchange for some good Y and you refuse to give me Y after you were paid X, then I should be able to prove (regardless of how you feel about it) that I paid X to get Y. Otherwise you can only ever transact with the people you trust which makes it unusable as a payment system. You have to protect the payer from a fraudulent payee.
Why, if I said I paid and you say I didn't and I release my side and you don't release yours then although there is not 100% proof you did not get paid it looks shady as hell.
You can either have privacy or you can have proof. You can't really have both. Which was why I also pointed out privacy might be better on L2.
If you don't trust me or I don't trust you then here you go it's all in public, if we do then it's the same transaction but on L2
Or a simple private / not private switch on L1. Whatever.
But if either side can disclose without permission of the other don't think it's private. It's just more limited visibility. -Dave