Okay. I'm now going to argue against everything I just said, because I am totally biased to take Testad's side, because he's Testad.
The first, is origins. What if Testad had already recruited her? Could I still import my Lhose? I would be very sad if not, because I love playing Lhose.
Well, simple! Have the joining player replace the existing Lhose, with the approval of the host! There's no reason the existing character can't just be dismissed and overwritten while the player is connected.
The second is quests. Journals tied to the save like in NWN2, they're tied to individual characters. And quest items aren't tagged as such, so I could just import a character with, say, a purging wand and bum rush the final boss. If I couldn't, then I would be very sad, since I use the purging wand for damage.
You're forgetting the fact that journals can already be shared! There's a "Share Journal" button at the bottom of everyone's journal, which is toggleable! Easy solution: automatically reset journals upon going to another world, and allow the player to have journals tied to both the world and player! Simple!
The third is that NWN2 had character files, where characters were neatly stored with all their info. In DOS2, characters are a part of the world, as are their relationships and euipment. In DOS2, the world is saved with the characters in it, as elements of the world. In DOS, this was more of a problem, because of how homesteads would conflict, but in DOS2 we have similar problems, like aggression flagging after attacking someone being tied to the character. For example, if I were to import my character who had their collar off, aggroed the magisters, and was The One, what would be preserved?
Well, if they can isolate player data into a file (which I see as likely to happen, as it will most likely be a prerequisite for customizable Arena characters, which is a goal of Swen's), then it can be done on a most basic level.
As for the collar thing, just leave it off! They'll have to avoid guards, but that's an inherent risk in getting it off. As for magister aggro and The One status, that can be lumped in with journal data - tied to particular combinations of both world and player (so, Aleithia, my megamage, would have journal #1 on my world, and journal #2 on Testad's world, allowing her to progress at the pace of the world, and not necessarily the transient player).