I like your optimism, but we really don't have the linebackers to run any of those defenses, save for a base 4-3 or a 4-3 under.
We don't have the rush backers for a 3-4 (yeah, we can "run it" but it's going to be a poor facsimile), and the situation at nose leaves a lot to be desired.
We don't have near the speed in the LB corps or the exterior edge rushers for a Cover 2 look.
We aren't going to be able to play man coverage unless we can generate pressure from rushing the passer. No one on our front seven, save the aging and declining Vrabel, has ever shown an ability to get consistent pressure off the edge. Tamba certainly didn't without Jared.
It'll be a good run defense next year, but we're going to get shredded by the pass. It's going to be ugly. A west coast or Coryell team would absolutely carve us apart.