Not saying that it will change things, but have you read
this article on Grantland.com?
It basically shows that, at times, the Patriots were using a 3-4 and a 4-3
on the same play.
They were using 4 man looks whilst implementing a lot of 2 gapping techniques and mixing their looks up yes.
The 4-3 Vs 3-4 debate is massively overblown and overrated. I've been yapping on about how it's going to be neither for ages now.
The Patriots use a 33 personnel 90+% of the time. When Ninko stands up on the line, what do you call him? I still call him an OLB unless he puts his hand in the dirt. More often than not he hugs the RB and plays containment but occasionally they rush 4 men with him.
What that Grantland article basically shows is what I suspected (without getting a proper look at any coaching tape), which was the Pats employ multiple schemes and techniques at once to throw teams off whilst using Ninkovich in different roles. He's that elephant player with great versatility.
The defense give off a number of looks; 4-2, 4-3, 3-4. It's the beauty of the 3-3 defense. It enables you to have a smaller, faster defense then traditional 4-3 or 3-4 defenses and gives you the chance to scheme mismatches the other way around whilst being able to rotate your looks without having to sub if you don't want to. When the Pats drafted Dowling it was for a reason; you need physical, lengthy guys with long arms and good hands who have the ability to play all over depending on the look. They need to be effective in man coverage, smart in zone and lengthy to tackle It's why I think the Pats will look to draft yet another one this year.
The 33 employs similar confusion as a 3-4..you can bring pressure from all over the place and, like Belichick does, plays with the DL techniques and alignments. The tradition 33 was a 'stack formation'...what Belichick does with it is uses it's versatility to show the different fronts and techniques he likes to do. You see mainly 4-2 whilst you can player with that 'rover' player by bringing him into the box. He needs to be a sure tackler as you'#re now effectively playing him as a 4-3 OLB...there's your 4-3 look.
We then saw that they can move in 3-4 looks with pretty much the same personnel later on in the season. There were a couple of occasions where they dropped Ninko back as a LB, brought the 'rover' up into the box and it effectively looked like a 3-4.
The reason we stay with this look is simple because of the advantages it brings forward. It counters the spread perfectly. You can adjust your defensive looks, techniques and other strategies simply by moving your pieces around like on a chess board without even needing to make a substitution if you don't want to.
We'll likely see the Pats opt for a tall, physical corner (Dennard, Trumaine Johnson, Josh Robinson are prime examples) who can play as another hybrid type corner able to play safety if the team asks them to. However, don't be surprised to see the Patriots opt for a roaming safety like Markelle Martin, George Iloka or even Harrison Smith, who showed the ability to be a free safety in combine drills. The Patriots aren't that far off when it comes to corners; if McCourty, Dowling and Arrington are healthy you have 3 of your 5 CBs, Chung is your 'rover' and then you only need an athletic free safety to cover the defensive backfield.
What really messed the Pats up last season defensively was Chung inconsistently being around for much oft he season. The most versatile player on your defense has to be the 'Rover'...he was it, and when he goes down and all you have is a second stringer in Ihedigbo, you're likely to struggle!