I know that EA are keen to strike a balance between people who just want to kick the ball about and others who crave ultra-realism (possibly) at the expense of 100% fun. It seems to me that the solution here is to increase the number of options that it is possible for people to vary. We already have the means to vary the game speed, difficulty & ref strictness, but I think Player Injuries would be something to look at also. At the moment, we can either have them "on" or "off" - and to be honest, when they're on, you sometimes wouldn't know it. If, however, we had options such as "Dennis Wise Ultraviolence", it would be possible to play as Man U and faithfully recreate the first 20 minutes of last year's FA cup final with some degree of realism, or for fun, the other way around. Variable duration of injuries would also be a good thing - think of the nightmare posed to managers by players like Nilis and Kewell, both of whom are out for some time.
This would mean the inclusion of more players per squad, but it seems that's what everyone wants.
Also (for the record), the ability to select stadiums for teams is a must (and if we're to have regular internet updates, more could be added). Also necessary (both for fun and for realism) are player substitutions by the A1 of the computer. In F2K, the opposition only change their squad if you kick 'em hard enough. What sort of example is that to set the youth of the world? They'll end up warped.