Caserio falls into the same category as Josh McDaniels, where there have been plenty of opportunities to move to a higher position with a different team, but the optimal team just isn't available. It's unlikely that Caserio will take the open spot, but it does imply that the end of Caserio in New England might come sooner in the upcoming seasons, rather than later.
Oftentimes coaches and front office folks who want to move upwards will put their names into the ring to determine interest and build their interview resume as a desired candidate. I believe Caserio's just starting to test the waters.
Caserio started with the Patriots in 2001 as a personnel assistant, before becoming a coaching assistant in 2002. He became a scout in 2003, followed by a rapid ascension to Director of Pro Personnel from 2004-2006. In 2007, he tried on a new hat as the Patriots wide receivers coach (and we all know how that season turned out). From 2008 until now, he's played as the Patriots Director of Player Personnel.
He's been a desired candidate for a few seasons, but no teams have really been able to pry him away from the Patriots. Hopefully Bill Belichick can keep Caserio around for a few more seasons, but a contingency plan will likely be put in place over the next season.
Caserio would be the third front office person from the Belichick/Patriots to make a move this off-season, following Scott Pioli (rejoining old friend Tom Dimitroff in Atlanta) and Jason Licht (new GM of the Buccaneers).
Update: SI's Greg Bedard speculates, and Boston Globe's Shalise Manza Young agrees, Caserio might be tired of Belichick overruling the scouts in the draft room. Belichick overruled the scouts when it came to drafted Laurence Maroney and Chad Jackson (scouts didn't like them, and Brain Daboll especially didn't like Jackson), as well as Jermaine Cunningham, Ras-I Dowling, Tavon Wilson, Jamie Collins, and Duron Harmon.
That's a pretty damning list of players where Belichick's overruled the scouts. While Collins and Harmon have flashed as rookies, the rest have been much less than desirable (understatement).