I don't have any specific soft-forks in mind. On chain privacy is a really tough problem to solve. For one thing there's a fundamental cryptographic trade-off where you either risk inflation or retractive total loss of privacy (perfect binding vs. perfect hiding, pick one).
At a more mundane level any advanced (compared to what we have now) cryptography makes auditing the supply more difficult, tends to need more block space, breaks pruning and might break lightning.