1. Injuries - Simply too many of them, this causes lots of upset for many, many players. Especially the ones that do not obtain extra tokens. Lowering the % chance of injury is programmable, right?
2. Friendly matches - Mutual agreement would solve this easily.
3. Scheduling - 2 matches within 30 minutes is just too much.
4. Selling players - The ability to cancel an auction of your own player after accidentally selling him or when you change your mind would be nice.
5. Friends on other servers - It would be great to be able to move to another server in order to play with friends/family. You could limit the # of times a team can transfer in order to not disturb balances too much, as every server is different.