Andrew Sonnanstine is yet to get a start and hasn't made an appearance longer than one inning this season; not the case for the other four contestants in the running for the final two rotation slots. Jason Hammel will start tomorrow, J.P. Howell has came out striking out everyone while not walking the house (5:1 in 2.2 IP), Jeff Niemann toiled through one inning of work on Sunday (33 pitches), and before today's game was called Edwin Jackson had thrown 5 innings of scoreless ball this spring with five hits, three strikeouts, and no walks.
What does this mean for Sonnanstine? The team has suggested he could be a reliever, and while that certainly strengthens the bullpen is it worth the shot the rotation could take? After all, most of us are expecting Sonnanstine to perform modestly well this year; perhaps 185 innings, maybe more, a sub 4.5 ERA with good K:BB numbers doesn't seem out of the question for the usual tough-luck starter last season.
Sonnanstine's approach and different arm slots during delivery make him a hassle to adjust to early on for hitters. His first time facing a batter in a game Sonnanstine's OPS against was .697, the second jumps to .882. His per innings splits suggest that he's capable of retiring all bats - particularly the weakest of the lineup given a .581 OPS against in the third - the first time through, but begins to struggle upon the lineup flipping.
Let's assume Sonnanstine is headed for the relief corps - pure conjecture on my part - that leaves the Rays with Howell, Hammel, and Jackson battling for two spots with the latter two out of options. The fortunate thing; and unfortunate thing for the said trio is that each was unlucky last season.
While some have a different view on what makes a pitcher lucky or unlucky, including Eric Seidman who details his method in an upcoming book, I judge luck based on balls in play average while taking into account the balls in play data.

The points I wanted to emphasis are in yellow; essentially Howell figures to benefit the most from our improved ground defense and that HR rate tells us either when he hangs them they bang them or that he's simply a bit unlucky from last year. Each had a few hits go against them, and while there's no guarantee that will definitively revert I can't see each of them replicating that type of bad luck again. The grouping also needs to improve on their K:BB rates, and if they can do so I see no reason why the Rays can't have five league average to above average starters.
Now that I've spent 500 words based on five (four) spring training games and the ultimately meaningless schedule of starters I think I'll end this by saying that while I may dislike the back end of our bullpen - mainly just Glover - I've got a strange sense of optimism that we'll find ourselves with a good season or two from an unexpected starter, one who's name might just be Sonnanstine.