The NFL someday will be running MY 4-2 defense
4 down lineman, 2 LBs, 2CB and 3 safties. Now the three safties are key, 1 free safty, 1 strong safty, and a safty that can play both.
First and 10, run formation: LBers play tight to the middle of the field, just behind DTs. With the 2 safties playing shallow to the LOS outside of the LBs, with 1 deep safty (free safty) over the top.
Now for second down and passing downs my 4-2 defense can be manipulated to conform any plays the offense can throw at it, plus stuffing the run.
The two short safties will have to be rugged by design,with good size.
Cheers