With the system built the way it is, "customization" can only come through the addition of unique items with unique powers and stat bonuses. Movement speed, stun, increased attack speed and everything else should be on the table.
Despite the developer's opinion that folks would not be allowed into groups without such equipment, such was never true in FF11. If anything, you were acknowledged as a "lucky bastard" to have killed the NM that dropped the item and
won your roll against the rng gods. No one ever told me to leave a party because I didn't have a kraken club, or an empress earring.