Let me provide you with a new perspective, one I hope we see this season and on into the future - the 3-3 defense, or the 30 stack in slang.
I first brought up the 3-3 way back in 2011 - before a Ron Rivera/Sean McDermott defense ever stepped on a field. And a fair amount of time happened before it became the dominant force you may consider it today. Some of it works better in a Denver style setup, where one OLB is a blitz guy on a high level. While Luke Kuechly made that a 2014 focus, and both he and Thomas Davis are efficient, make no mistake, neither are Greg Lloyd or Von Miller.
But, in a coverage setup, even in man, a 3-3 makes sense.
In personnel, it brings all three linebackers on the field - Thompson, Kuechly, and Davis. The concept being, Davis and Kuechly were excellent at coverage (bears out in metrics, too), but they struggled a bit to deal with a slot TE. Or, to use a Saints style conundrum, they couldn't cover easily both Jimmy Graham and Darren Sproles. Luckily Sproles was let go in New Orleans, and that had an easy time against Graham with Davis,
In true man, it's a matchup situation. By having all three LBs on the field, you have some size - maybe not perfect against the run, but you're not exchanging a 3rd corner for either a SS or your SLB (which is, once again, Thomas Davis). You have a LB that can go in space, and a LB that can cover a player that comes out either side of the backfield.
You can still play Cover 1 Robber, a two - zone, levels defense that has the FS in deep zone, and usually the SS or MLB in under zone (i.e., you play man, but you have help inside no matter what), a good play against 21 or 12 personnel (2 backs 1 TE, 1 back 2 TE), but a danger against either personnel with a split TE or back (the back isn't often crucial, but consider that Matt Forte last year had more targets than Greg Olsen, and almost as many as Kelvin Benjamin, on an offense that had Alshon Jeffery and Brandon Marshall).
This graphic is out of base, and that'll happen a lot, but consider that zone with nickel, too.
So, I don't know. A 3 man line diminishes a bit of what Carolina does best, rush the passer, but if they play as much man as they had in the 2014 year, and have added a matchup piece in Thompson, why not a 3-3? You keep your nickel, you keep your SS, and you keep your matchup piece.
A 3 man line rotation, along with Carolina's tricky double-A Gap pressure (along with its fakes), seen below:
and suddenly you have a lot more options than McDermott or Rivera have ever had.