Posey is really quite bad now. He's just a contract, maybe a couple minutes here or there. If Boston traded for him they'd have to get another valuable chip in return, as at this point taking Posey's contract away is the favor; you have to give him with an asset to get teams to take him.
To afford it, now that Sheed is gone (still disappointed, even moreso now, because it definitely seems like Ainge could have wiggled his way into the 4 way deal that just happened), the only way to be able to take back Posey would be to package Davis with a re-signed Scal at the old 3 year but only 1 year guaranteed deal that starts at about 4.2 million or so. Now, one intriguing deal, now that Indiana is thick at the 3 spot but thin at the 4, would be Baby/Scal for Posey and Rush, if Indiana would do it.