I think we need to separate the impact of Nix as an individual from the physical profile one needs to excel at NT.
Nix is a first-round talent, and he's been a huge part of our recent defensive renaissance. Anyone seeking to diminish his contribution to this title run deserves to be ridiculed.
Conversely, there has been much hand-wringing over the fact that Nix is a prototypical NT and that we have no one else resembling his physical profile on the roster. It has certainly been a concern for me as well, but upon further reflection, it seems a silly thing to worry about.
ND's coaching staff has known Nix would be likely be gone after either the 2012 or 2013 season, and yet they haven't managed to recruit anyone else like him. Given their success at recruiting and player development, I have a hard time believing this is the result of failure or incompetence. Hell, we allegedly had a chance to take
Tommy Schutt and
turned him away in favor of
Sheldon Day, an explosive pass rusher who does not fit the NT prototype.
Since Kelly's arrival, we've seen several different body types playing Diaco's 0-tech: Ian Williams (6'1'', 305 lbs), Sean Cwynar (6'4'', 285 lbs), Kona Schwenke (6'4'', 290 lbs), Tony Springmann (6'6'', 300 lbs), and Louis Nix (6'3'', 340 lbs.). Nix has obviously been the best, but how much of that is due simply to his physical profile?
Our coaching staff does not seem to recruit separately for DE and DT. Instead, the strategy seems to be the same as on OL-- recruit athletic "Bigs" and see where they shake out later. The most athletic prospects play OT, and the less athletic prospects get moved inside to OG.
Similarly, our most athletic DL tend to play DE (because they do a fair amount of pass-rushing), and our less athletic DL move inside to focus on two-gapping. If they've got the frame and a good work ethic, Longo can mold them into immovable objects. Nobody foresaw Schwenke and Springmann at NT, and yet there they are.
I'm starting the ramble here, so I'll quickly get back to my point: the staff clearly isn't concerned with finding another prototypical NT, so we shouldn't be either.
And that's no knock on Nix; there's bound to be some drop in positional productivity whenever a 1st round talent leaves. But we're probably getting worked up over nothing here.