Been playing FM since the 2007 version so got a few good ideas-
Improved press conferences and clearer consequences- Press conferences get tedious having to answer the same old questions again and again with the same answers not knowing the effects it has on the players.
Training upgrade improvement- Instead of just improving levels in training facilities, we should be able to buy equipment and facilities to improve on certain aspects of training e.g swimming pool to improve strength and stamina traing
Potential abilty- Get rid of it! In the real world you can't predict the maximum potential of a player. It's annoying nurturing a player from the age of 15 then hitting his maximum potential. Any young player should have the potential to be a good player.
Rivals- I play as Chorley who's rivals are Bamber Bridge, Lancaster, Accrington and Preston. The problem is, when I take Chorley to the higher leagues I rarely ever play rivals. Change the rivalry system to change based on the club status and manager comments.
Junior teams- In modern football major teams train players from the age of nine. It could be interesting and very satisfying to spot a young star early on and train him to a world class level.
Player friendships- Allow players to randomly develop friendships with team mates other than just tutor and learners friendships.
Random events- Players falling out with each other after a string of bad results, hitting the headlines after non-football incidents, high profile players getting advertisement deals etc etc
Testimonial games
Thats just off the top of my head for my first post