This is a really good one
Allow you to control just one player! Like if I make a created player, I want to be him his entire career (but still play as a team) then if I become unhappy as a created player I can request to be traded, I can decline to play for another team (I'll never play for the clippers, but my team wants to trade me, so another team needs to be brought it)
Kinda like a dynasty for me!!
This one is probably the hardest to do, but I think it would be the coolest!
What do you think? Maybe add this to the list and send it down to EA!!