Persistence preset: I2P
There are good reasons for making I2P's data dir persistent but the most imporant one is that it'll be less wasteful in terms of bandwidth when bootstrapping.
/var/lib/i2p persistent would enough for this. It could have a preset made for it and perhaps be enabled by default.
I think there would be fewer hurdles to jump over in order to enable this than there would be for Tor. For example, none of the I2P scripts rely on non-persistence.