Some things I feel are needed in Nostr and could be build reasonably fast:
- onboarding micro-app (so that the next Snowden would give a single link with proper UX) - a simple wizard that asks user proper questions and guides to create profile, choose client, LN wallet, etc
- actual approved functional iOS/Android app, big question whether native apps will be approved even w/ 'block' buttons, maybe some hacky unobvious path is needed
- upload media (audit/video/images) on major client on shared, hopefully decentralized infra
- basic spam/profanity suppression in major clients, most probably by temporary switching to 'safe' relays
- search built into major clients, supported by several relay implementations
- custodial LN wallet built into your client to dramatically reduce friction for noobs
- remote signing with a single (mobile) app for key-storage (not quite sure it's 'easy', but from proposed NIPs it seems doable)
- embed-post widget so that people on the web could embed nostr posts like they do with twitter
- share-on-nostr button, which launches proper client or onboarding experience, to be used by members of community on their websites
- comments widget for websites, to be used by members of community
- online-chat, to be used by members of community who run online businesses
- tools for local communities to run/bootstrap/feed custom relays