Let's look at the three players the Astros just acquired, shall we?
Jonathan Singleton
Singleton was a Philadelphia 8th Round pick in the 2009 draft, and was largely considered to be Philly's top prospect (FanGraphs puts him at #2, behind Domonic Brown). He'll be 20 in mid-September, is 6'2", 215lbs, and was Baseball America's 39th-ranked prospect coming into 2011.
In 2009, he played 31 games for the Phillies' GCL team, hitting .290/.395/.440, with 13K:18BB. Playing for Lakewood, in the South Atlantic League, in 104 games he hit .290/.393/.479, with 74K:62BB in 2010. In 2011, he advanced to High-A Clearwater, where he was hitting .282/.386/.411, with 14 doubles and nine homers in 378 plate appearances.
The question is about his defense. Singleton played first in 2009 and 2010, but has split time between left field (30 games) and first base (45 games) in 2011. It could go either way: The Astros could put him back at 1B, since Mills can't trust Brett Wallace to even think about a left-handed pitcher.
Of course, they could just make Singleton a full-time outfielder. With J.D. Martinez' call-up, there's a gap. And if Singleton can hold it down in the outfield, he could start in LF in 2013, when Carlos Lee is mercifully off the team. If the Astros thought too much of J.B. Shuck, he would have come up to Houston instead of Martinez.
I also wonder if he will move to the corresponding level, which would be Lancaster. David Flores has been playing 1B for the JetHawks, and is hitting .325/.385/.577. Kody Hinze was recently called up, and is flat-out killing the ball, hitting .348/.410/.623 for Double-A Corpus Christi, in 19 games.
Of course, they could just make Singleton a full-time outfielder. With J.D. Martinez' call-up, there's a gap. And if Singleton can hold it down in the outfield, he could start in LF in 2013, when Carlos Lee is mercifully off the team. If the Astros thought too much of J.B. Shuck, he would have come up to Houston instead of Martinez.
So here's a guess: If the Astros keep him at 1B, it's unlikely, but possible (as OremLK notes, he's only 19) he could go to OKC, and put pressure on Brett Wallace, effectively ending Koby Clemens' shot at Astros glory. If the Astros move him permanently to OF, he goes to Corpus and takes J.D. Martinez' spot.
UPDATE: He's fared much better at 1B than in the outfield, so let's call him a 1B.