There's a consensus in Bitcoin that the main next step towards better privacy is using Schnorr signature, but in the last few years there were multiple security

There's a consensus in Bitcoin that the main next step towards better privacy is using Schnorr signature, but in the last few years there were multiple security issues found in the Schnorr signature based multisig protocol (MuSig). After each improvement the devs prove the security of the protocol and present it in a cryptography conference, asking for peer reviews, that's why it's moving so slowly (which is great).