I agree that trying to build "everything" on Nostr is a bad strategic error. Specially when these things are even more dependent on network-effect than a microblogging social network (like uber or Nostr, for example) or when they depend on private communications. People have been trying to do this since day one, though, it's just something wrong with the mind of developers.
But I think tools that are "social" in nature and mostly involving publishing human-scale content in the open but don't require that the entire world is using them in order to be useful (like geocaching, for example) are good niches through which Nostr can expand.