I think Payjoin can be a very good privacy solution for Bitcoin, but I have a question about it:
– If a user has 1 BTC and make a payjoin payment to other person of 0.1 BTC, the other person can see in a blockchain explorer the change address with an amount of 0.9 BTC. That's a serious privacy leak. I would like to know what will be the standard solution to this issue. An easy fix could be that the user wallet check if any address contains a BTC amount higher than a "safe" amount like 0.1 BTC or less. If some address exceed that amount the wallet could automatically make 1 payment to itself to split the amount in several addresses. In this way nobody receiving a payment from a user will ever know that he has a bitcoin balance higher than the "safe" amount.
What do you think?