I'm sorry if this has been suggested before, but I'd very much like to see more emphasis in commentary and match-buildup concerning players who are playing their former teams and the like. Things like 'he scored against his former club' are nice, but there have to be a lot more options. People facing off against favourite (or disliked) staff of theirs and more attention for statistics against your opponent would be a lot of fun. I think it would be great to see rivalries and friendships between players and teams given more depth.
It'd be great if it would be possible to sign a player on a bosman six months ahead, then have the flexibility to try and sign him right then and there. You see this happen in football quite regularly, but when you sign someone in FM, you'll have to cancel the upcoming transfer to try and buy him outright.