From Matthew Kory:
Nobody has mentioned Castellanos in rumors, not that I’ve heard of anyway. But the Tigers are out of it, they need to sell JD Martinez, and they’re probably not far from flinging whatever isn’t nailed down out the door. Castellanos is sort of nailed down, but maybe. He’s a former first round draft pick, selected by none other than Dave Dombrowski, and he’s the toolsy sort of guy you’d expect based on the first part of this sentence. He’s not a great fielder, but he’s under team control through the 2020 season and, here’s the kicker, he’s crushing the ball. According to FanGraphs, Castellanos is making hard contact 49.6 percent of the time! That’s insane and way above what he’s done in the past. Yet, his BABIP hasn’t shown it yet. Part of the problem is his 41 percent ground ball rate, but if he starts hitting the ball in the air with that kind of contact, this is a guy you would want in the lineup. So maybe the Sox take a shot with a guy like this hoping the improvement shows up sometime upon reaching Fenway.
He doesn't seem like he's much of an upgrade, if any, and his defense is not good. I only bring this up because he's a Dombrowski guy so maybe he's on Dombrowski's radar.