I hope Styles and Nakamura stay in NJPW (though, I would most certainly mark out if they did pop up on NXT or the Royal Rumble). I just don't have the faith in the WWE that they'll do anything significant with them in the long-term.
I think Hunter's just bringing top indy names in to generate buzz and positive feedback about himself, and then if we're lucky, a guy like Kevin Owens will eventually get called up, find early success, relegated to the midcard, and might eventually be promoted to main event jobber for Reigns.
I shudder to think of Nakamura in the opening-card comedy act Tajiri role, or Styles in the current Dolph Ziggler position. Better they stay in NJPW and be the big fishes of a smaller pond.