I'm sure the Sox will bring in a utility guy who can play the left side of the infield, but it won't be some great "backup plan in case Middlebrooks struggles." That's not how it works. Billy Beane used to say you spend the 1st third of the season figuring out what you have & the 2nd third of the season trying to make improvements where they are necessary. Trust me, there is not going to be a "serious contigency plan." By the way, if the Sox Front Office was so "down" on Middlebrooks, they wouldn't have told everyone who asked that he was unavailable at the deadline. My "guess" is that the Sox Management understands that he had a serious wrist injury, he may have started believing his own hype & he's not the first player in MLB history who struggled to make adjustments as quickly as the "fans" wanted him to.
If Middlebrooks is brutal, they'll likely make a move for a stop gap 3rd baseman, but again, if he's here, he's going to get a long look at 3rd. They aren't moving him to first, they aren't moving Bogaerts off of SS & they aren't bringing in a guy who can start over the long haul in case Middlebrooks fails. You can keep posting this stuff all the way through spring training, but "realistically," Middlebrooks & Bogaerts are going to be starting on the left side of the infield. They aren't going to rotate 4 guys at 1st base & they aren't overly concerned with Ortiz getting an occasional rest in NL parks.
I know they are not going to rotate 4 guys at 1B., but there may be 3 guys in the mix at ST, if we don't sign a FA 1Bman plus Papi for some NL games.
A lot depends on Nava's need in LF. If we sign Beltran to play LF, then Nava will platoon at 1B with Carp, and Middy stays put at 3B or is traded.
If Nava is needed in LF, and we sign a decwent SS, then a 2 man platoon at 1B could occur: Middy/Carp with Carp getting some time at 3B vs some righties as Bogey sits or as Bogey backs-up the new SS.
I'm not talking some wild and crazy 5 way rotation and platoon.
Again, as I have said many many times already: I do not think Ben or Farrell are thinking along these lines. I expect they are planning on Bogey at SS, Middy at 3B, obtaining a decent utility IF'er and rolling the dice. If Middy struggles, they can trade for a 3Bman or SS and adjust if needed. If Cecchini is ready by mid-season, we may see him take Middy's slot.