Although I've not watched a lot of Ferdinand this season, I think it's telling that Fergie sees fit to pick Evans and Smalling ahead of him on a regular basis. If he doesn't think he's either good enough or fit enough to keep them out of the team then I can't see Hodgson being too concerned about making room for him in the squad when he has younger centre backs who he's going to need to cement into 'the group' for the qualifiers and hopefully tournament in the summer.
I've never been much of a fan of Johnson but I think he gets quite a bit of unfair stick these days for his defending. It's as if, like David James before him, he's unable to shed the reputation built in his early days. Look back at last weeks game and the Euro's and Johnson is usually in the right place at the right time and has made some important covering tackles, blocks and goal line clearances. There are a few other options who will put him under pressure, but I think he's probably got the spot tied up unless Walker gets and takes a chance soon.
There's obviously the main threat Walker, who is another with a reputation for attacking over defending, then Jones and Smalling who should both mature into centre halfs but may find right back their short term role. There's also Martin Kelly and the young lad Wisdom at Liverpool who look decent enough and the forgotten man Micah Richards (I still think he can come good), with another long term prospect in Jenkinson. Coming through below that, but not quite there yet, are Clyne and Chalobah who I think has been used as a right back quite often now.