So the resulting game design challenge is: come up with a game setting where it is impossible for one player to bog down another. Scene A and scene B can each take as long as they take in real life, and in the game world once they're wrapped the players can decide which happened first or if they happened simultaneously (the latter a necessary possibility if what's happening in one scene could theoretically affect the other.)
The first setting which occurs to me is a game where the characters are artificial intelligences capable of forking themselves and merging again. AI Alpha needs to be in two space stations simultaneously, so it copies itself into Alpha-1 and Alpha-2. Alpha-0 stays home. Alpha-1 and Alpha-2 travel to the appropriate space stations and return home; Alpha-0 does a merge so that it has all three sets of memories (staying home and going to both space stations) so that Alpha-0, Alpha-1, and Alpha-2 are identical, then deletes the others.
Note that with virtual reality, this setting isn't restricted to high technology: the AIs could be programmed to think of themselves as mages in a fantasy world, telepaths in any setting, whatever -- and the underlying virtual reality could support the illusion. Given players comfortable with the underlying setting, though, you could do pretty much anything in pretty much any style (i.e. moderated or GM'd, consensual or roll-based, whatever.) However, if the underlying reality is stipulated as AI and virtual reality, the game won't work unless the players are comfortable with thinking in terms of AIs, virtual reality, forking, merging, et cetera.
There are other sorts of characters which could logically be in two places at once -- gods in some mythologies, perhaps powerful telepaths, people with bilocation as a freak talent.
I can easily see a game where the characters are all gods, perhaps from the same pantheon, perhaps from rival pantheons, perhaps some of each. My instinct says the natural gaming style would be consensual results for most interactions -- that is, I don't think it would be wise for the game mechanics to decide when Athena or Ares win a fight with each other, but either win fights with Aphrodite every time, and either loses fights with Zeus every time. You could do GM'd if you can find plots for gods that aren't basically rivalries with each other. Moderated with a focus on character-character interaction and plots secondary and largely player-driven wound be easier.
A game where the gods are characters would default to being timebound to Earth - that is, Athena might be in three places at once, but "at once" would always correspond to a specific date and time. You could tack on something in the way of uncontrolled or semi-controlled time travel, or stipulate that when the gods separate pieces of themselves they don't fully control when the pieces rejoin, to work around that and decrease the need for scenes to happen in chronological order.
A game where all players are telepaths cloning their minds is harder. Doable, I think, but -- do you set it on the astral plane and have no real world to start with? (If so, you'd need players that are very patient with getting the game started, or lots of players, or both.) Do you set it on Earth with the accompanying increased timebinding ... perhaps with the limitation that you duplicate your mind and it travels through astral space to get elsewhere on Earth, and the duplicate may have a hard time finding its way home and rejoining you? I think that could work, if the players are all interested in playing telepaths.
A game where everyone has the ability to bilocate I'm not really sure what to do with. Maybe include in the bilocation ability the ability to remerge with the limitation that if you use that to teleport home you might remerge with your other self right now, or a month from now, or a year from now. Tack on limited communication (low tech level, or multiple dimensions, or separate solar systems united by the bilocation, or whatever) and you can easily meet the challenge; the potential genres could be anything, and so could the game styles.
All of the above ideas make the simultaneous threads work by limiting the character types. They could be interesting games ... but is it possible to make the challenge work by make the simultaneity a property of the setting rather than the characters?
In order to make a setting where everything can happen in any order, we need to break chronological time. This could be any universe which had a timequake that wasn't resolved, but I think things work best if this is a dream world. In an actual physical world things happening out of sequence prompt too many other questions which need to be answered in order to help suspend disbelief. In a dream world, this could be the normal state of things: two people dream about you simultaneously, and you're in two places at once; one dream ends and another begins, so A and B happen simultaneously, then D and Q, then C and F.
That said, I think an asynchronous game set in a dream world would work better if the dream world were broken. If you break the dream world, perhaps the characters aren't (or don't have to be) natural inhabitants of the dream world. You could design a game where the characters are all from the real world; all from any fictional world; full panfandom with characters from anywhere with or without fourth-walling privileges; or near-full panfandom with a preferred genre (that is, characters can be drawn from anywhere because reality has broken down and is recreating things from elsewhere or dragging them here when dreams intersect, but the dream world in question is being dream up by dreamers from one world in particular and that dominates the way the world works, both in terms of genre and in terms of the way NPC characters and abilities work (to take an extreme example, many worlds have faeries or elves, but they're very different from world to world; PC faeries could be from anywhere and be anything, but NPC faeries would be from the dominant world.)
Anybody have any thoughts on any of the above possibilities? Other possibilities to suggest?
Cross-posted to ecreegan.dreamwidth.org at http://ecreegan.dreamwidth.org/5086.htm