SIP-121: Support for L2 Synths

Simple Summary

Provide support for sETH, sBTC, sLINK synths in addition to sUSD on L2. In addition to these 3 synths more may be added in the future.

Based on a front running risk analysis, the price feeds on L2 Optimism Kovan were deemed to be lively enough that fee reclamation can be removed all together on L2, without increasing the risk on SNX stakers. That being said, mainnet will be monitored and should the Spartan Council find that fee reclamation should be switched back on it can quickly be re-enabled.

Abstract

This SIP proposes adding support for the following synths on L2: sBTC, sETH, sLINK.

Motivation

Without adding more synths to L2 users are stuck holding sUSD and cannot participate in trading other synths. Use cases like futures and shorting require support for multiple synths beyond sUSD. Bringing leverage to L2 is one of the major strategies of Synthetix and in order to offer a good product experience for our users we'll need to support many synths. Additionally when liquidity pools like Uniswap V3 become available on L2 it will be beneficial to the protocol to capture liquidity incentives in synth pairs beyond just sUSD. For example cross asset swaps between sUSD, sETH, amd sBTC should be quite beneficial to offer near zero slippage.

Specification

These Synths will be implemented in the same way as the other Synths on L1. This includes adding or updating the following:

Deploy a contract for each synth we're adding (sETH, sBTC, sLINK).

Including the Proxy, Synth, and TokenState contracts and connecting them together.

Update ExchangeRates which then uses the associated Oracle Feed for each synth listed.

Add commentary on feeds and ExchangeRate.js.