In no particular order, a few:
- Key setup more like a bitcoin wallet with a mnemonic phrase and a backup step, and a recovery process if that key were lost.
- Non-complicated and simple relay configuration, paired with an in-app marketplace for relays and other services that add clear value: long-term storage of notes, lightning/ecash wallet services, media and etc.
- Invitation system to bootstrap various suggested WoT for suggesting notes and profiles to follow. This could be topical relays!?
- An illustrated in-app explanation of why Nostr is awesome. 

 all good improvement ideas. thanks for sharing!