This proposal is about persisting additional data in the LeaseSet that is currently ephemeral. Implemented in 0.9.18.
In 0.9.17 persistence was added for the netDb slicing key, stored in i2ptunnel.config. This helps prevent some attacks by keeping the same slice after restart, and it also prevents possible correlation with a router restart.
There's two other things that are even easier to correlate with router restart: the leaseset encryption and signing keys. These are not currently persisted.
Private keys are stored in i2ptunnel.config, as i2cp.leaseSetPrivateKey and i2cp.leaseSetSigningPrivateKey.