This will be debated, of course. But the very fact that Kelly - the leading college practitioner of the up-tempo, read-option offense - seems to want to go to a 3-4 suggests that he believes it is the most effective counter to his offense. That only makes sense. Besides, it isn't as if the Eagles are loaded with great 4-3 defensive players who will have to be discarded during the changeover.
With that, we begin with a look at what they have. The quick conclusion is that the transformation will take 2 years, minimum.
Nose tackle: This is an enormous issue because it is really hard to make the 3-4 work without having the quintessential 3-4 nose tackle, the athletic big slob who can routinely occupy at least two offensive linemen, a guard and the center, and to do his best to control both of the A gaps on either side of the center.
Looking at the Eagles' roster, there is only one guy who could even think about playing the position - Antonio Dixon. But at 6-3 and 322 pounds, well, he wouldn't be big for a nose tackle. He also has been a journeyman player, at best. They likely would have to find a guy here.
Defensive end: Fletcher Cox is as perfect a fit for the 3-4. His size is exactly right for a 3-4 defensive end - 6-4 and 298 pounds. He is big enough to wrestle with offensive tackles, tall enough to see into the backfield, athletic enough to command attention from the guard. He was a rookie in 2012, and he sometimes/often played like a rookie, but there is plenty to work with here. Besides, you can't fire everybody.
But who would play on the other end? This isn't a pass-rushing position in the 3-4 and it isn't a glory position. Instead, it is the lousy, difficult work of tying up offensive linemen so the linebackers can make the plays. It is really hard to see either Trent Cole (6-3, 270 pounds) or Brandon Graham (6-2, 265 pounds) playing this position, or anyone else on the roster. They likely would have to find a guy here, too.
Inside linebacker: The Eagles probably have this part of it covered with DeMeco Ryans and Mychal Kendricks. There has been a lot of misinformation put out there about Ryans and the 3-4. The way the story has been written by some, the reason that the Texans were willing to trade Ryans to the Eagles was because, as they switched to they 3-4, they determined that Ryans could not play as a 3-4 inside linebacker. But a fair reading of the situation reveals something different.
The reason they were willing to move him was money, not the scheme. When offenses go to three wideouts, one of the inside linebackers in the 3-4 generally leaves the field - and the Texans determined two things: 1) that Brian Cushing was not leaving the field, meaning that Ryans would have to become a two-down player, and 2) for salary-cap reasons, they weren't willing to pay elite money to a two-down player.
It was the money, not the skill. Ryans played almost 100 percent of the snaps last season for the Eagles and played well. He could be the more rugged of the two inside linebackers in their new 3-4. The other guy, who gets to run around a little more, could be Kendricks, who showed some great athletic flashes as a rookie.
Outside linebacker: In a 3-4, these are the flashy playmakers. Looking at the Eagles roster and trying to figure out who they might be is a total head-scratcher. Logic suggests that Graham would get a long look here, although it is more than fair to wonder what he would look like chasing a running back in pass coverage. It is far from a sure thing - and the same would be said for any experiment involving Cole and/or Vinny Curry. Maybe Kendricks could be one of the outside guys, with Jamar Chaney and/or Casey Matthews playing one of the inside spots.
There is a lot of what-iffing here, obviously. But the Eagles are likely to need at least one new outside linebacker to think about making this work.
Secondary: Most everybody thinks the Eagles are going to need four new starters here before they are going to have a good defense. This is another discussion for another time, but it is really hard to imagine Kelly looking at the recurring haplessness perpetrated by every member of that secondary in 2012 and coming to the conclusion that, by golly, these are his guys.
With that, add it up. Two cornerbacks, two safeties, one defensive end, one outside linebacker, one nose tackle.
Seven new starters.
Two years, minimum.
On Twitter: @theidlerich