A wholly original client. There’s an overpopulation of the next Twitter replacement etc. General population won’t move or stay until there’s a client that offers a unique experience.
Many consider the npub/nsec transition to be a large hurdle. I think it’s an opportunity to have a more seamless user experience in the future. Where you can move through clients like your walking into and out of a store on Main Street. People hate having to create new accounts for each thing.
Another hurdle is that Nostr places the onus on the user to curate their own experience. Some people want moderation and curation. They’ve become accustomed to it. They’re used to having an online experience where their hand is held. So getting users to take back their locus of control is a shift even for those building. User experience has long focused on how they can make a user do something. You won’t get to a wholly original client with that mindset.