I don't think the ask is that outlandish?
I'm not saying that I'd do it, but Castillo is really good.
Maybe in this case, it's not too crazy, but the general idea that Torres would be available is very 2017. He's not a hot prospect anymore, he's a starter for the Yankees.
Also, I think Castillo is being overrated just a bit. He's older than people think he is (27) and has a 10.4 fWAR over the last four years. Over the same period, Tanaka has a 9.1 and has been outstanding in the postseason, and he's expendable.
Castillo is cheap and controlled, yes, but you don't trade your starting shortstop who hit 38 homers last year because a guy is cheap and controlled.