Shortly before the 2015 Rule 5 Draft, Chris Mitchell at FanGraphs shared the results of his KATOH model that projects major-league WAR for minor leaguers. Mitchell describes KATOH, named after Yankees prospect Gosuke Katoh, as "a computer-based statistical model that produces long-term, major league forecasts for minor league players."
It analyzes factors like a player’s walk rate, strikeout rate, home run rate, rates of singles/doubles/triples, and stolen bases and adds in soft factors like age, whether the player was drafted in high school or college, and position. Mitchell doesn't pretend KATOH is the be-all-end-all, but because it's objective, it can identify "talented players who might be overlooked by the scouting consensus for reasons unrelated to their on-field performance.