I prefer abstract rewards for teamplay rather than more gamey/forced rewards. ATM you do get extra XP and gold if you help your team to win, whether thats by flanking, being in a group, standing miles away pewpewing etc. If people feel they need to get near a banner they might not be as imaginative or might not do whats actually in the team's interest to win. Also leachers are better off not encouraged to get too close to the main players because they will block swings, team hit, get in the way, try to survive etc. If someone is going to leach, at least get them dead or out of the way sooner rather than later imo
I'd rather some kind of expansion to the commander system, its not really used as it should be atm. Possibly some more things like the + shield skill for shield walls. There is a funny assumption that only melee need to play together too, why not encourage ranged to play together, or cav? Why should they have such good damage/range that enables them to play more solo than melee? Why do they have such good melee capability, if they had to relly more on their melee team mates they would be playing more like a team. Why do HA get away with just riding around randomly by themselves?