I don't think I have to be encouraged to use Hive more. But I'll try and answer this on behalf of the average social media user to the best of my ability.
I think the critical element is ease of use and great UX (User Experience, there's a difference between that and UI). If that means third party custody of private keys, then so be it.
Using Hive has to be ADDICTIVE and FUN. Monetary rewards will by necessity be a distant secondary concern. The UX of the major apps has to be designed by serious professionals and it has to involve a lot of testing and community feedback. Everything has to be as SMOOTH as possible. The learning curve has to be as flat as possible.