It would be a "huge" upset if the Rangers put Neftali Feliz into their rotation, according to Bob Nightengale of USA Today (Twitter links). However, the Rangers are aware that next year's free agent class is loaded with top relievers, so they'll likely move Feliz to the rotation for the 2012 season. Ken Rosenthal of FOX Sports points out that trading for a closer at this point in the spring is difficult and argues that Feliz belongs in the bullpen.
Rangers manager Ron Washington said earlier in the week that he wants an experienced closer. Feliz, though still 22, closed for Texas last year when the Rangers made it to the World Series, so he qualifies. Other established closers like Heath Bell and Joakim Soria don't appear to be available.
Bell, Jonathan Broxton, Matt Capps, Francisco Cordero, Brad Lidge, Joe Nathan, Jonathan Papelbon, Francisco Rodriguez, Rafael Soriano, Jose Valverde and other top relievers could hit free agency after the 2011 season, at which point the Rangers would have many more options than they do now.