I know some or all of these suggestions are probably not realistic to implement into the game, but I though I'd try to throw a bunch of things up there, and see what sticks:
I'd love to see some changes to the trophy screen, in order to include individual players stats as well as some club stats. For example, the "player wing" of a team's "museum" could include stats like most goals or assists in a game, season, and career, or even broken down into league, CL, and cup. Individual stats like most caps, longest tenure with the team, and highest transfer/salary paid would also work well. As far as the club, stats like best/worst losing/winning streaks, largest margin of victory, and highest overall team salary would work well.
Another suggestion would be for the stadium and team facilities: make them more customizable. I'd love to be able to use my team's colors in elements of the stadium, to use them as the color of the seats or stadium fascia, for example. Further, it would be awesome to select from different aesthetics of the stadium - clean and modern, ornate and traditional, or an intimidating dungeon. To take that concept even further, different "styles" of stadium could affect performance in different ways - lower chance of injury vs. amplified crowd impact vs. reduced opponent morale. Plus, more team customization is always more fun
Lastly, less ambitiously, I wish there was a time preference for matches - I'm in the eastern US, and I've had matches at 4:30 and 5:00 in the morming. The ability to set preferences for match times, within reason, before the season starts would be a welcome convenience.
I realize my suggestions are probably difficult (or worse) to implement, but I figured I'd try to think creatively... hope someone agrees!