This call registers and onboards the Polkadot People Chain with all the Identity info taken from the existing state of the Relay Chain. The runtime is based on v1.2.6. The release notes include instructions on how to generate the genesis state and also contain a chain spec for node operators.
Note for wallets and UIs: Once the People Chain is onboarded, UIs should fetch Identity info from the chain and stop using the Relay Chain. Deposits will be migrated with the enactment of 983.