Instead, the Rays designated Miller for assignment in order to make room for first baseman-slash-outfielder Jake Bauers, who will be making his big-league debut:
So far in his age-28 season, Miller has hit .256/.322/.429 (109 OPS+ while seeing action at both first and second base. He sports an average or better stick against right-handed pitching, but offers next to nothing against lefties and is a negative on defense -- albeit one who has played all over throughout his career.
The Rays now have a week to trade or release Miller. Given his relative youth, low cost (he has an additional season of team control remaining), and track record (he's not yet two years removed from a 30-homer effort), there's every reason to expect him to land elsewhere -- perhaps with a contender like the Los Angeles Angels, even.
Bauers, who the Rays acquired in the Wil Myers trade a few years back, won't turn 23 until October. Baseball America had him down as the 45th-best prospect in baseball entering the season thanks to his above-average offensive potential. In 2018, he'd hit .279/.357/.426 at Triple-A.
It's worth noting that Bauer's promotion comes a week after the unofficial deadline for Super Two status.
For those wondering, most ballplayers enjoy three years of arbitration eligibility before they reach free agency, with those years beginning after they've reached three years of big-league service time. The top 22 percent of players with between two and three years of service time qualify for Super Two, which grants them a fourth arbitration year. Almost by rule players never make their market value through arbitration. As such, that additional year can get them closer to earning what they deserve based on the market and their play than they would otherwise.
In other words, by waiting as long as they did to promote Bauers, the Rays succeeded in manipulating his service time just enough so as to suppress his earning potential over the next six years.