Well, I hate to tell you but Milani and Koerner will be in the mix as well. Don't be surprised to see Koerner backing up Stone at FS next year. Milani is kind of like Ward last year. Not the greatest athlete, but they trust him.
I agree that some people are going to have to provide some depth at the safety spots next year, I just don't think we can know who that will be. I think Castro is a smart kid who is similar to Stone and may work his way into the equation as a freshman like Stone did. We love us some HS QB's at safety. I can go back a long way, but more recently, Snyder was a QB, Hooker played some QB, Gervase was a good QB, Stone played QB, etc... and Castro plays QB. I don't expect this trend or tendency to change.