Jesus Montero never got the 'untouchable' banner during his ascent through the Yankees system, and so when they dealt him to the Seattle Mariners for sophomore star pitcher Michael Pineda, it registered as only a moderate surprise. If The Washington Nationals traded Bryce Harper, or if the Tampa Bay Rays traded Matt Moore, it would not be a moderate anything. It would be a seismic event.
Untouchable prospects get talked about less and less lately, largely because the value of prospects in trade has gone sky-high in the past decade. Teams grab the best prospects they can with every intention of keeping them, and have come to expect more and more for those guys. Therefore, virtually anyone can be had, but only at the right price.
There are exceptions to that rule, though. Here are the prospects in each team's system whom other clubs might as well write off, because they are not going anywhere. For a bit of spice, look for the notable absence from each team's list, too. Those are the guys who might just get dealt.