The Great Script Restoration
Introduction
The Great Script Restoration is an undertaking started by Rusty Russel and it aims to re-enable most of the Script opcodes that were disabled early in bitcoin's history. In addition to re-enabling the lost opcodes, it also aims to add a small set of new opcodes to further make Script an ergonomic and powerful scripting language for expressing smart contracts.
A large part of the work is focussed on developing a cost function to safely express the cost of each opcode used in a transaction's Script, so as to avoid denial-of-service (DoS) attack vectors. The risk of DoS was a large motivation for the disabling of these opcodes at the time, so great care has to be taken when they are re-enabled.
One of the opcodes that this project would re-enable is OP_CAT.
Specification
Pending BIP and implementation.
Implementation
Rusty is working on an implementation, but is also seeking help from anyone interested to work with him on this project.