The only guys who get crosstrained at Safety, are the ones who were already a Hybrid Safety to begin with.
OJ hasn't taken a snap at Safety, neither has O'Connor, or Lucas, or Antoine. And among the incoming Frosh, Waters, Portis & Jennings are staying at Corner.
Its just Dunnigan & Fritz really. None of the other Safeties are getting reps at Corner & technically speaking, playing Nickel is essentially the STAR/3rd-Safety spot anyway.
Safeties and Corners are different; just like DT's & DE's are different, just like Mike's, Will's & Sam-Backers are different.
No need to muddy up the CB thread with a bunch of Safeties, they got their own thread.