Ok so I'm reading up into this to try to get a feel, excuse any mistakes you see as I'm kind of jumbling a bunch of knowledge together but please point them out.
First of all, this isn't a strict diablo clone I expected, maybe that's smart, maybe that's incredibly dumb, we'll see.
I'm not sure if the campaign has you with all 4 characters all the time, for argument's sake lets say it's always a foursome. You have your single player character. He levels, earns skills and equips loot you find just like any other game in this genre.
Now you want to host online for a friend, you have to make a new character, because your first character is tied where he is in the story. You can't use him for multi-player anyway, I don't think, but even if you could you CAN NOT bring him back to the beginning of the game. So you host a game for you and a friend online, you decide to play one of the other three characters and your friend randomly picks one. After a few hours, you tell him you're tired and get off.
Now, he doesn't get to keep anything he's done on that character when he disconnects from you, but when he joins you again, that character should be the same as he left him(or auto leveled up if you've played without him). Meaning, he is playing a character on YOUR game file and ON your file, he has the same build and equipment he had before, but this is tied to your online play of your second character. None of these characters can interact with your singleplayer save nor can your friend migrate his character he's been playing back into his own singleplayer or another multi-player game.
Every single version of a character, whether on a multi or single save file, is unique and non-transferable. This is why I'm thinking of the multiplayer as some kind of single player addon. If you were for instance playing FFXIII, and could have a friend join you to play as snow for a few hours, it would be similar. In your game he's snow, and he might choose what skills to level and what equipment to wear, but when he leaves you he doesn't get to take that with him. That snow character is still stuck on your save, on your singleplayer game path though the game. You can't import him to another console nor import him to another place in the game because in your save file, he is at a specific part in the story, and must stay there.
Not only that, but like in FFXIII and in this game, you CAN NOT have more than 1 character per save. If you wanna play the sword wielding guy, you're it, no one else can be him. Again going back to the idea of singleplayer/story mode trumping any kind of multiplayer/co-op, at no point in the story is snow cloned so that the party consists of 3 snows.
I think it's an interesting way to think about the game, but it is flawed in every single level of it's execution. The entire game becomes an arcade experience. Insert a coin and press start to jump in with a stranger at any point in their game, but as soon as you leave, you lose everything you've done with them unless you play with them again. Even playing with a friend is only somewhat better as if the host plays without someone else, they just completely miss parts of the game as that character but atleast auto level. If they want to play and the host isn't around/doesn't want to/hates the game, they have no way to access a character they might've spent 10 hours on playing with the host.
I hope in one of the ways I explained it, it makes sense. This is from late april, I can't imagine it changing much since, but I'm going to read a bit more..
