In 2007, Justin Jackson was selected as a shortstop out of high school by former Blue Jays general manager J.P. Ricciardi in the first round-supplemental in the amateur draft (45th overall, compensation for Frank Catalanotto). Before the 2007 draft, Jackson was very highly touted by Perfect Game, receiving a perfect 10.0 score, and being called "one of the rare legitimate five tool prospects."
Unfortunately, his hitting in the minors have been lackluster, having a career .230/.320/.315 line. The Blue Jays tried to convert him into an outfielder starting in 2011. In 2012, he split his time between playing shortstop for Dunedin (A-Advanced) and playing centrefield for New Hampshire (AA). After a .255/.310/.289 line in 66 games with the AA Fisher Cats, he was asked to put down his bat and focus on his arm, which has been his best asset. Jackson (@JaxChillinONE), a Twitter enthusiast, made the big announcement himself:
Ladies and gentlemen I will be PITCHING in 2013 can't wait!!! #newchangenewthangs— Justin Jackson (@JaxChillinONE) January 6, 2013
Not sure all the pitches I will have next year it's a work in progress— Justin Jackson (@JaxChillinONE) January 7, 2013
Jackson's Instagram account shows pictures of him pitching in the 2006 Aflac All-American Game (probably before or after the game; he was on the roster as a shortstop, and the left fielder is facing the wrong way) as well as him working out this year. When JaysProspects spoke with Jackson back in 2011, they reported that he had thrown as fast as 93 mph back in high school. According to Jackson himself, he was clocked on 95 on a relay throw from second to home in 2012. Perhaps harnessing the power of his arm on the mound could turn him from a failed prospect (according to Emily G) into a Major Leaguer.
Until he starts throwing in Spring Training (which starts in less than two months!), there is no way to know how good he could be. Justin Jackson is just 24-years old, so it is definitely not too late to make a transition. Current Blue Jays reliever Sergio Santos, also a first-round shortstop, was an infielder all the way up to AAA, and didn't start pitching until his age 25 season. Having been one of the rare examples of a successful conversion, Santos may be of big help for Jackson's new direction. Santos spoke of his transition to MLB.com back in 2010 here. Trevor Hoffmann made the same transition from shortstop to the pitcher's mound at age 23, and he turned out pretty good. Of course, for every successful convert there have been many failures.
Another Blue Jays farmhand in the middle of a conversion is Matt Johnson. He was the Vancouver Canadians' shortstop until late June 2012 when he was abruptly converted to a pitcher mid-season after a mop-up appearance during a blowout. In 15.2 innings with the Canadians, Johnson recorded a 3.45 ERA, a 1.404 WHIP, striking out 17 while walking just 5. Marc Hulet took a look at him as well as other conversion projects at FanGraphs this past August.