This may be difficult but can you link it also to the stats of the player/s above them on the depth chart as i'm sure an RB would be more accepting if he had to wait behind Adrian Peterson than if he was waiting behind a lesser RB ?

Brock Osweiler just left the Broncos because he was upset that they played Peyton Manning in the Super Bowl instead of him, and got a huge contract (can I say way overpaid? Kind of felt like I was watching an MFN offseason there). I think the player who is willing to play second fiddle to a better player when he could start elsewhere is the exception and not the norm.

His expectations are based on his current ratings, not his future ratings. So a draft pick won't get as upset as he is developing, but once he's fully developed he will want to play.

Will there be some correlation between degree of injury and playing time and how that effects the feeling towards an owner? Like say will a player that is probable dislike being inactive or getting minimal playing time as say someone who is doubtful?

Yes, if a player is not healthy his unhappiness about playing is relative to how hurt he is; a questionable or doubtful player will not get upset as much as a probable or happy player will.

I just checked my roster and I have one player who has always been a starter but he's unhappy...Is this by design? Can we always expect 1 or 2 players who will never be happy no matter what? (If so, I actually like this too) Maybe the player wants to play closer to home or something like that!

I like the idea, BUT have reservations about it. I still find hiring coaches bad enough without the headache of egotistical players.
I think you need to be more specific as to what would keep a player happy and what would turn him into a diva. Simply being 'unhappy' and we have no idea how to please the little prince is unattractive.

I would agree with AZ. Working on updating the coach aspect of the game would help in the overall game.

I have a rookie TE who is already unhappy only 5 games into the season he's second on the depth chart is there some randomness to the speed at which different players change opinion? The second year player who got bumped down the depth chart behind him remains happy?

Just wondering if playing for a team with a winning record has any impact on how happy/unhappy a player is ?

How much you win or loose has no impact on whether a player is happy or unhappy with you. Its all about if he plays and/or starts for you. Injuries also play a part.