Taproot would improve the privacy and fungibility of Bitcoin transactions. It seems Smart contract payments, Lightning payments, and sophisticated multi-signature smart contract payments all look the same after Taproot. When Taproot does eventually roll out, it is likely to be followed by more incremental protocol upgrades. Graftroot, which delegates signatures to allow for additional multi-sig functionality.
Please let me describe the building blocks of Taproot for better context.
The aim of Taproot is to ensure that Pay to Script Hash (P2SH) transactions appears indistinguishable from other transaction types therefore improving privacy and scalability. There is a proposal within Taproot to replace EDCSA with Schnorr signatures and therefore allow signers to jointly produce a signature, rather than needing to compute independently and add to the transaction.
Taproot also introduces Merklized Abstract Syntax Trees (MAST). MAST looks to provide additional privacy for complex redeem conditions by hashing the various potential routes. Taproot aims to use MAST in order to hide all conditions for spending and reduce the size of this information. Taproot uses MAST to include the merklized hash as the public key, thereby then includes making a complex script transaction indistinguishable from a standard P2PKH transaction.
The introduction of MAST within Taproot improves both the scalability for complex redemption conditions as well as transaction privacy by obscuring the existence of alternative routes. Please find an interesting write up on Taproot, MAST and Schnorr Signature here.