One thing that is deserved to be said is that no matter what privacy-oriented concepts, ideas, techniques are implemented in bitcoin, you can never achieve the same levels of privacy in comparison with privacy-oriented cryptocurrencies. The reason is simple: Their privacy model is enforced by default*, whereas in bitcoin, privacy enhancement is optional. Stones are set from genesis, and even though Monero (which is what takes the cake)
experienced leaks on privacy, it still forms the best black-box-like electronic money out there, in sum.
*Z-cash excluded?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.
If you give me cash, and I don't give you weed, you can't prove you gave me cash. Yet, it's working fine centuries now.