T.R. Sullivan has a blog post up in which he seems to suggest that the Rangers' rotation for the start of the season is now set, and breaks down as follows:
This splits up the lefties and splits up the two righties with similar repertoires, which makes sense.
Of the other starting pitcher candidates, Tommy Hunter looks slated to start the season on the d.l. and Neftali Feliz looks likely to start the season in the bullpen. Derek Holland will, I imagine, start the year in AAA, although he could fill the 2nd lefty in the bullpen role (particularly given that Rule 5 draftee Ben Snyder got hit hard in a minor league game today).
That leaves the question of Brandon McCarthy, and at this point, I have to wonder if he isn't going to end up getting dealt before Opening Day. He seems like a questionable fit in the bullpen, he has to clear revocable waivers to be optioned to AAA, and he's pitched well enough when healthy that he'd appear to have some trade value. You have to wonder if he doesn't get offered as part of a deal for a quality UIF or righty bench bat in the next couple of weeks.