I think Mayer will be a damn good player, but the injury concerns are just too high for my liking. Our need for a 2Bman, and maybe a SS, once Story leaves, as well as 3B depth are major issues on this team, so trading away a kid like Mayer is very risky, but I'd be okay with including him in a trade for someone like Ryan, Skenes but probably not a Keller type.
We have too many OF'ers, so I have to think one gets traded. We could also trade KC and/or Mayer and roll the dice with Romero and Arias as eventual depth or replacements to our infield. If we trade all three, our return should be very nice. If we add pitchers like Sandlin, Mullins, Early or Clarke, we might be able to make 2 big trades.
The next step would be to somehow get Yoshida off the 40 man, but parking him in AAA could be an option. I think we keep Casas as a DH option, because his trade value is close to nil, but his potential is an .850- 30 HR guy.