I would like the single player career mode to start at grass roots. You have to play for your local sunday league etc and play on bad pitches in the park etc. You have to be discovered by scouts, not like at the moment where I am a striker and do not score, but Man Utd still offer me a job.
I liked the playing in the reserves that they had a few years ago, maybe extend that and have to play in the youth team when you first start. They should also put in that you can be fired for not being as good as they want, lets say you go into Man Utd academy and you are no good enough when you first start, you get fired etc.
Career mode, you should be able to apply to any managers job, at the moment you can only apply for jobs in your league (or abroad). I am a Port Vale fan and when I have won the league with one team I might want to become Vale's manager, but because they are two leagues down there is never the option.
Real injuries, If you make three subs at the moment, no one will then get injured and have to go off. Make it realistic and have injuries that can happen no matter how many subs you have made.
Diving should be in there, its part of the game and like it or not its part of the modern game. It can add to the fun of playing your mates. One of my fav games was This is football, due to this. Time it wrong and you are getting a yellow.
Real refs, at the moment they have sub human ability to tell what happened. If they are not close enough, like in real life they will have to guess. Sometimes they will get it wrong again adding to the realism