I find my in Madden always gravitating towards a "theme team". I would absolutely love for them to have some attribute perks for rocking theme teams. Have some different levels or allow us to customize our teams with certain styles.
Like New York Yankees: Power perk
If you have 10 Yankees in your lineup they get +1 power or something.
Then add speed/contact perks
The main reason I like them: it would take a guy who is clearly one step below the "meta" player for a certain position and elevate that person to being more comparable.
You could obviously go into more depth with this as I just gave a small example. It would just add that nice bonus to those who are diehard fans and want to use mainly their team players.