Hopefully we'll still be able to launch multiple instances of the game and create our own Multiplayer game to create custom parties.
That shouldnt be a problem, acording to (feel free to corect me if im wrong) what Red Queen have seen on Larian life presentation.
If i remember corectly, Swen just took another controller and created another character on fly.
Yes, in the presentation I saw, Swen swapped into split screen coop and created a second custom character on the fly (this capability is mentioned in the update) and then when the second player left the game their custom character was still there in the party of the first. But I am not sure that was actually meant to happen, or that it would happen on release. Swen actually reloaded to before he'd created the character. So I'd say this
might be a possible workaround for completely custom characters, but we shouldn't be totally confident.