Have it so that any goal scored by a player is recorded so that you can view how many goals you have scored with a player. This could be repeated with other stats, such as saves.
More challenges to do as a league. I can't really give an example but it would make the leagues have more purpose if you could all work together on an objective, rather than just a league pack given by goals.
Another idea could be to expand on the friendlies feature. I would like to see something where you could play against someone where you could choose any player in the game as appose to your team. It would be nice to try out the likes of Ronaldo in a casual match against a friend.
Personally I think the reward for a donation is too low. I see so many people request for players and tend to not get much XP. This is because there isn't a real incentive to donate players. There could be weekly donating objectives where you could receive an exclusive pack for reaching a certain amount of donations.
In game addition:
I think there should be a button to bring your keeper out to the edge of the D. In 5-a side matches keepers typically lurk around the edge of the D when the opposition is near to narrow the angles. I know that the keeper can come out, however this is AI controlled and I feel the player should be able to have control over their goalkeeper.
I know there are quite a lot of ideas so I don't expect them all to be added. But I firmly believe these additions would take the game in the correct direction and freshen it up.