I'd give up a great young pitcher for those 4. I probably do it for 3 of these guys, however only if I was a non-contender.
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The problem is twofold and may be insurmountable:
1) There are only a handful of teams that pretty much know they are not going to be winning a championship in the next 3-5 years and would be willing to trade any immediate hope they have at a near championship to greatly improve their odds at winning 3-5 or more likely 4-7 years from now. (Teams looking to win in the next 1-3 years will not look to trade an ace for better extended hopes.)
2) Of these handful of teams (maybe PHI, ATL, SDP, MN, OAK & CIN), not many have an ace-caliber young pitcher under team control for 4+ years (counting 2016) at a reasonable cost?
You want specifics? If I was Billy Beane, I'd trade Gray for Swihart, Benintendi and Swihart. I don't think Devers would be needed, but maybe Owens or Johnson might be added. I'm not sure what Phily would want for Nola or Eickoff, but I'm not sure if either of them project as an ace. There's a lot of talk abour Teheran of the Braves, and if I was their GM, I'd trade him for 3 of those guys, but if I was the Sox, I'm not sure I would. I'd give Swihart, Devers and 2-3 mid-level guys but not 3 of our top 5 prospects. The other teams don't have anyone I think meets our needs.
I seriously doubt we can lure a contending team to deal an ace without giving something MLB ready and of near top quality.
As much as I hate to say it, I think what I want might be impossible to get.