RSK is a sidechain to the Bitcoin chain. It exists for 4 years now and its traction is getting bigger and bigger.
RSK started to push forward on its Defi protocols and we see more and more protocols joining it along with infrastructure protocols (Chainlink for example).
It's worth supporting.
Environment
We're a team of several protocols that are using your amazing upgradable contracts and also using Harhat to manage all the deployments (upgrade proposals) and tasks (custom action proposals).
We would like to manage everything via our RSK Gnosis safe, and in order to do it right, we would like to use Defender to perform our upgrades and run our hardhat tasks.
So until it's supported, we cannot use it.
Details
Lack of support by Defender 
RSK is an EVM-compatible chain, so adding support to it should be simple enough.
It also has the rsk-gnosis-safe.com interface, so also using Gnosis with Defender should be an easy task to add to the system.
Its main block explorer is this one: https://explorer.rsk.co/
Would really appreciate Defender's support here