Absolutely. Next release of yana is in the works, and will feature an outbox model which will fetch notes from your contacts only from a small number (configurable) of relays. And also will cache recent events on local db, taking special care not to let it bloat out of proportion like other clients. It's a fine line to find the best balance between network data usage and device storage but I agree it is very important for people with restricted data plans and older devices with limited storage in less privileged places in the world. So it will be our focus developing it.