I would be concerned that, because of the softness of PVC, you are going to get increasing play in the pair of gates over time as the steel post and the weight cantilevered off it grind away at the inside of the pvc each time the gates swing. You are also going to have droop from the onset even with what you call a small amount of play.

Why do you need posts that are easily removable? I'd concrete in sturdy, galvanized posts and attach hinge mechanisms that won't wear out like your PVC sleeves.

One other thing. I came upon a gate that looks to be a pipe-in-a-pipe swivel, like you are thinking about, but the swivel is aboveground. Below is the link...see what you think.

Here is a link that might be useful: Hingeless gate

Hi, If your thinking maybe you are going to put up a gate sometime, a couple of ideas . Pour around the place where you post will be then fill the empty part with decortive rock or pour the drineway and seperate with expansion joints where your post will be. You also could pour the driveway and if you decide to put in a gate in rent a hammer drill and about a 6" concrete hole saw.
Woodbutcher