I have a few suggestions based on playing FM for past few years and also other Sports SIM's such as OOTP and FHM which whilst not offering the depth of FM in some aspects they offer much more in other ways. Also as social media and the almost constant flow of managers in clubs at all levels its possible for a manager to be running more than one club in a single season such as Rafa Benitez at Real Madrid and Newcastle.
Also more and more than ever before players become more involved in issues which may ultimately effect Morale, Form and even team selection a bad comment in the press, a tweet taken out of context even photo's driving sports cars can effect fan sentiment and a hero can quickly go to zero fan power is bigger than ever. I suspect FM going forward will be making these influences far more important and for realism this is highly relevant.
In addition other ideas I have are...
1. Being able to load historical data such as the teams of years gone buy Class of 92, Arsenals Invincibles and maybe even the Busby Babes, Cloughies Derby and Forest, The great teams of Milan, Madrid and Barca and even the golden days of Ajax .
Presumably the actual players would be a matter of public record so it would only be a case of adding the option to change data and start dates to run this as an add on or option for additional content. To see how this could work look at OOTP Baseball which takes historical teams for over 100 years and allows the player to re create the seasons and nostalgia with those teams. A little more off the wall is taking teams of yester year say the undefeated Arsenal team (invincibles) and pitting them against those playing currently.
2.Another thing I would like to see is being able to actually take over a current team and manage the team as the current manager for example instead of say PEP Guadiola getting the boot at Man City you could run the team as PEP and see how you would fair in the role with the same team etc. Again this would require a data change but in principle just changing start dates should make that possible it would be case of taking over a club on a given day if this could be possible?
3.It has been said there is no such thing as an un known talent these days with modern scouting, and software meaning even a 10 year old will once on the radar be monitored at least by some one.This being the case contrary to being a "newly discovered talent" the reality it's a case of who signs them first. Case in point being Anthony Martial or Rihyad Mahrez they appeared to have come from know where but it transpires this isn't really the case. The tracking aspect of FM isn't that apparent what would be great if a team needs a forward with certain criteria and over time a player achieves or is believed to have the potential to achieve that where as previously they hadn't the program offers the manager a suggestion to consider .... X player not sure if data can be used dynamically like this so may be not possible?
4. More needs to be considered regarding how revenue is generated teams like Man City have rich owners but produce less advertising revenue than say Real Madrid and Man Utd who have more revenue streams such as sponsors etc. This dynamic is more and more relevant as player wages go higher and transfer fees of relative unknowns become almost limitless. Some teams have better negotiators than others and even factors like the weather, a girl friends preferred home and competiveness of league seem to effect player choice. A less robust player might be harder to attract to say the Premiership.