A great post at Rany on why Soria would likely be especially valuable as a starter.
Closers have the bonus "leverage" of working in swing innings, and thus are 1.5 to 2 times as valuable per-inning as starters. But starters still eat up innings and set the tone of games.
The typical closer increases in ERA 25% when moved to the rotation. But Soria might do better than this. He has great control, and a tremendously low batting-average-against. Furthermore, his low isolated-power-against also bodes well for getting out of jams when pitching 6 innings--avoiding the 3-run homer.
Rany notes that even if his "real skill level" is closer to 3.0 ERA than 2.48, treating the 25% increase as an upper bound (due to his good control) would put him at 3.75 ERA, making him on par with Meche and Banny.
The Rany arguments make it almost unthinkable that he won't be moved, I should think.