A Curry/Ball tandem really wouldn't be beneficial to either player. Ball doesn't have a ton of off-ball skills and him being the third option in GS wouldn't be the best place for him to go, nor would it substantially help Golden State in the next few seasons. It would be nice to have a secondary ball-handler, but ultimately Golden State is going to want the ball mostly in Curry's hands and for a team that is trying to win right now, they wouldn't have the patience to deal with Ball's growing pains, of which there would be a lot of even for a talented young point guard. Wiseman did not have an awesome rookie year, but having a super-athletic 7 footer that can block shots and also flashed some shooting touch was a worthy pick at #2, even Ball was a technically better player.
I can't think of too many times where a great team successfully bridged from one era to the next. I guess the Spurs going from Robinson to Duncan, but Duncan was an all-time great talent right from the get-go so that is incredibly rare. I think most teams with cores like the Warriors are more interested in picking up one or two more big guns and making another run at a title, not wasting time and assets to develop a post-Curry future. When they eventually blow it up, they will have earned an enormous amount of good will with the fans and can go into a true rebuild mode for a few years.