It'd be a real hard sell to transition that defense back to a 3-4. They're 10th in defensive DVOA and 6th against the pass.
If anyone has the Cardinals rated as the 10th best defense right now, they need to fix their rating system. I don't care what factors they're taking into account - they're wrong.
This team is horrible against the run, and extremely bad overall. They're 6th worst in points allowed per game, and dead last by a mile in rushing yards allowed. OK, technically not by a mile, but by over 500 yards worse than the median team. The only reason they're any good at defending the pass (they're 5th in passing yards allowed per game) is that no one needs to pass when they're up by 30 points (they're 7th in fewest pass ATTEMPTS per game).
They're also 5th worst in takeaways.
No one with working eyeballs and brains believes the Cardinals D is 10th best in any way, shape, or form.
...dbs