I think Bo Jackson might end up being the reward for completing all 32 teams
Other than that I would like to see:
John Randle or Jared Allen (Vikings)
Either or both of the LTs (Chargers and/or Giants)
Marshal Yanda (Ravens)
Von Miller (Broncos)
Julius Peppers (Panthers)
Jason Taylor (Dolphins)
Also since I switched to Raiders theme team it would be cool to see who the Raiders get, Bo Jackson as the base set would be cool but I think it's more likely he ends up being the overall reward because of how popular he is, and he usually gets a card every other year that is insanely overpowered and hard to obtain.