Latest status here. There are still 2 head coaching vacancies, at franchises that would be regarded as level 2.
The strange thing is that there are a large number of former NFL head coaches out there who presumably are still of employable age, yet most of them are working in television and/or on their golf handicaps. Increasingly, a lot of former NFL head coaches seem to have no intention or interest in doing the job again. Here is a quick off the top of my head list of former head coaches who are currently sitting out, playing golf and/or working in media:

Brian Billick
Bill Cowher
Tony Dungy
Dennis Green
Jon Gruden
Jim Fassel
Mike Holmgren
Steve Mariucci
Eric Mangini
Jimmy Johnson
Herm Edwards
Mike Martz

That none of the above seem to be publicly interested in a return to the NFL suggests that the job of NFL head coach is one that many of them found to be insufficiently compelling, despite the large financial rewards and prestige. It also seems that Jon Gruden has not attracted any serious interest, despite him being the youngest of the potentially available coaches.
NFL teams have a disturbing tendency to go for the latest bright shiny object in coaching, and coaches and co-ordinators tied to currently successful programs will always have the phone ringing come hiring time. This approach does not work too well a lot of the time, since from the outside it is often difficult to determine the underlying contributors to the success of a coaching and personnel program. In the past 5 years, Notre Dame, Kansas City, the New York Jets, Cleveland Browns and the Denver Broncos have all found out that hiring members of the Patriots "brain trust" did not lead to any sustained success. Whatever the real method and leadership approach is that operates within the New England Patriots, it is likely that it is more based on process than personalities, the whole is much greater than the sum of the parts, and plucking individuals from the operation and expecting them to be successful elsewhere was way too optimistic an approach.
There is also the reality that many lower-level coaches and co-ordinators do not have the correct personality and approach to ever be successful head coaches. In the early 1990's, Norv Turner and Dave Wannstedt both became NFL head coaches on the back of the success they enjoyed with the Dallas Cowboys as co-ordinators. Based on their records since, I would submit that neither of them is really a top-flight NFL head coach. We then got to see the same phenomenon unfold at the Cowboys as Jerry Jones, after splitting with Jimmy Johnson and winning one final Superbowl under Barry Switzer with Johnson's team, proceeded to promote his assistants to Head Coach one after another, only to discover that there was a good reason that no other teams had previously hired them away to be head coaches.
There is also the phenomenon that some people interview better than they perform and vice versa (in playing terms, think Tim Tebow vs. Kyle Orton at Denver in 2011 - Orton practised better than he played, Tebow was the reverse). Gregg Williams apparently wowed his way into the Buffalo Bills as their head coach largely on the strength of his job interview, yet that did not translate to success in his new role, and he has been a defensive co-ordinator since, up until the bounty scandal made him radioactive.
Aside from the Eagles hiring Chip Kelly, the most intriguing hire is that of Mark Trestman by the Chicago Bears. 15 years ago, Trestman was regarded as one of the great offensive gurus in the NFL, yet for unknown reasons, he fell off the radar for head coaching opportunities, and ended up moving to the CFL, where he has been highly successful. As this article explains, the lack of NFL interest might have something to do with his demeanour, rather than his methods. Every QB who ever worked with Trestman has, almost without exception, raved about his abilities, so Jay Cutler must be quite happy about now.
At present, neither the Arizona Cardinals or the Jacksonville Jaguars have hired a new head coach. It is likely, that with "no interviews" windows in place for some co-ordinators, that those teams will not finalize their head coaches until close to the Superbowl, which will leave them short of time to perform pre-draft evaluations and planning.
It is also likely that in 3 seasons from now, half of these newly hired coaches will have been fired, and this process will be starting over again. As Kurt Warner once said, NFL really stands for Not For Long.
In the NFL there are only two types of coaches; those who have been fired, and those who will be fired.
UPDATE - In a stunning reversal, it is being reported that Chip Kelly will become the head coach of the Eagles after all. And, a dysfunctional deck-shuffling is unfolding in Dallas, as coaches leave the Cowboys. I sense the interfering hand of Jerry Jones in all of this, and it will not end well. The current process is looking more and more like an exercise in scapegoating to cover up the deficiencies of both Jerry Jones and Jason Garrett. If it continues, it is going to leave Jason Garrett looking like a "lame duck" coach, in the same category as Dave Campo and Chan Gailey, since people inside and outside the organization will conclude that Garrett is no longer in commmand as the Head Coach, and is merely taking orders from the owner. It is also destroying continuity in coaching, which is an important success factor for teams in the NFL. Monte Kiffin, excellent coach though he may be, will be the third defensive co-ordinator for the Cowboys in 3 seasons.
If I was Jason Garrett, I would be looking at the head coaching vacancies right about now...