Hi all, I am a NNS researcher working on the SNS.
To avoid misunderstandings, I just wanted to clarify that an initial version of all SNS canisters is already completed. As you correctly state, the ledger canister will use the same code as the NNS ledger canister. The governance and root canisters can be found here.
As you can see on our roadmap, we are working on further evolving these canisters and also provide better support for the initialisation and upgrades (see for example this forum post regarding upgrades). So if you would like to use an SNS that is deployed on the SNS subnet and maintained by the Internet Computer as a system function, this is planned for the Carbon milestone. However, you can definitively already look at the canisters’ implementation and start implementing against the APIs! You can even self-deploy an SNS with a governance, ledger, and root canister on an application subnet and try it out!