PLEASE allow SS's to return kicks; in fact, why not allow any position to return kicks as in real life? It would be cool to see a backup athletic QB, for instance, who wants to help the team and goes out for punt return. Some day it'll happen...
Much more important is to let SSs return. If you let free safeties, why not strong?

I can check on this, but tbh the game engine will not handle SS returning kicks all that well since typically WR, RB, CB have higher speed, higher agility, etc.