Tim had an interesting idea earlier this afternoon:
I actually think that Locke/McPherson will be the #5 starter even if Liriano is healthy for Opening Day.
My initial reaction was that this didn't make much sense. With A.J. Burnett, Wandy Rodriguez, James McDonald, Francisco Liriano and Jeff Karstens available, there would be no need for Jeff Locke or Kyle McPherson to start the year in the rotation if everyone were healthy. The more I thought about it, though, the more likely it seemed that Locke might break camp as a member of the starting rotation. (Let's forget about McPherson for a second -- I wouldn't rule out the possibility that he could make the rotation, but he has very little Class AAA experience, so I think it's less likely in his case than in Locke's.)
Karstens' inability to stay healthy was part of the reason the Pirates non-tendered him, and probably also part of the reason they got him back so cheaply. On top of that, check out my last build of the 25-man roster -- the likely bullpen currently features several inexperienced pitchers in Bryan Morris, Vin Mazzaro and Justin Wilson. That's partly because Morris and Mazzaro are out of options. But it wouldn't be surprising if the Pirates wanted more experience coming out of the bullpen. The bullpen might also be easier on Karstens physically, so it would make sense, on one level, for the Pirates to send Wilson to the minors or to DFA Mazzaro (who the Pirates likely wouldn't miss a whole lot) in order to put Karstens there.
That way, Karstens could pitch a few innings a week, also pitching multi-inning stints if needed, and then rejoin the rotation if someone struggled or got hurt. If the Pirates don't see Karstens as a 180-inning pitcher -- and there's no reason they should -- then this would be a way to make good use of him while still having him pick up 120 or 140 innings.
Placing Locke in the rotation would also have some merit, as long as you have a good backup plan, as the Pirates now do. Locke did well in Class AAA last season, and showed much-improved command in his six starts in the majors. He also tended to make big mistakes, leading to six home runs in 34.1 innings, but he can probably improve in that area as he gains experience in the majors. (Some bad luck contributed to his high home run total as well, and his HR/FB ratio should regress to the mean in 2013, improving his numbers.) Locke has a good chance of being a credible starter in the majors. I didn't like the idea of having him begin the year in the rotation when there was little to fall back on, but having Karstens (and Liriano) around gives the Pirates a good deal of security.
All this is moot if Liriano or someone else isn't healthy, of course.