CastroW is a combination of young enough, cheap enough, and versatile enough where exposing him to different coaching might be worth keeping him around for another season. Didn't Harris say they were looking for a RHH OF and LHH IF? He's a switch hitting utility hitter. Maybe that's all he'll ever be.
But keep in mind the entirety of how the roster is composed. If they go with 13 Ps, they'll carry 2 Cs and 1 DH only (when Cabrera is healthy). That leaves 10 guys to cover 8 positions. Baez will play everyday, and hopefully Meadows too.. I imagine Greene and Torkelson would ideally be playing everyday. If so, they're down to 6 guys to cover 3 positions, but keeping in mind that Baez/Greene/Torkelson/Meadows will need a day off here and there, but probably more taxing will be Cabrera not playing everyday. Although assuming 4 everyday players, with 6 covering the remaining 3 positions, that shouldn't be an issue. Just to be clear, I don't assume Schoop returns next season, but I would imagine that he plays everyday if he does return.
Does CastroW still have options? They could stuff him in Toledo to see if his game improves if they have they wiggle room on the 40 to get him there.