Next year, between the majors and AAA assuming no trades, you're going to have Mullins, Hays, Santander...McKenna and maybe Stewart. Neustrom has performed alright at AAA. Stowers will likely move up. Watson is starting to look like a prospect, walk rate be damned. It's getting crowded and Diaz will need to earn time.
I suspect Santander will be traded, and none of the guys you mentioned are top prospects so there is a spot for Diaz.
Hopefully they find DJ Stewart a home somewhere else too..