Miller has split time between Double-A and Triple-A this season, and has hit the ball well at both levels. Miller hit .356/.426/.596 in 122 plate appearances for Triple-A Tacoma, and hit a solo home run on Thursday to extend his hitting streak to 22 games in just 26 games played.
John Sickels of Minor League Ball is a big supporter of Miller despite his relative lack of notoriety:
Miller is one of the best infield prospects in baseball in my view, but for some reason he's never received quite as much attention as he deserves...He controls the strike zone well, shows good power for a middle infielder, doesn't strike out that much, and has had no problems adapting to advanced minor league pitching.
There is some concern that Miller will not be able to handle shortstop defensively for the Mariners, but Seattle is confident that he can stick at short. Miller will join fellow rookie Nick Franklin as the team's starting middle infielders.
The Mariners are expected to option Carlos Triunfel back to Triple-A to clear space for Miller. Brendan Ryan, who has hit .196/.254/.252 in 236 plate appearances, will serve as the back-up utility infielder.