There were lots of times in the previous Divinity games where I debated which piece of equipment was better, given roughly equal damage/armour and slightly different bonuses. In D:OS even if two characters use the same build and same weapon type, it is unlikely they would have exactly the same preferences for bonuses, so it wouldn't be terribly hard to sort out the loot (second best probably being pretty close to best in quality most of the time). Even if someone got two upgrades in a row better than what the other person had, then the first upgrade would get handed down to the other player.
The game needs to be balanced for 2 main characters and up to 2 henchmen. There is not going to be a case where someone is walking around with a broom and nails pounded into it, and a pot on their head, because they got into a few conversations, while the person they were playing with went out and looted the only good equipment available.
Apart from that it will be pretty boring (and hard!) to play with two fighters, two rangers or two mages....
