At various points I've mused on the possibility of setting up an "Open Tabletop" - a game where there is no expectation that any given player will come to any given session but where it can go ahead regardless, provided there's a quorum of players. It strikes me that I've actually taken some steps towards this with my current "Firefly: the Lost Episodes" series, although with the caveats that I mentioned in my previous post - that it would be better for people to use their own custom characters rather than the crew of Serenity. (The crew of Betty works as an interim step, but even that's not quite ideal.)
Firefly is actually an ideal game for this concept, since the game doesn't have too many fixed roles (so you don't run into problems if no Cleric shows up), and since each session constitutes an "episode", thus allowing for some shuffling of the pack between times.
But I did have one problem with the construction: if you want an Open Tabletop, ideally you want it set up so that any member of the group can drop in or out as they wish. And with there being sixty members of the group, how do you square that with a Firefly being able to transport maybe a dozen in even cramped quarters? Not to mention that there are only half a dozen or so crew positions?
After some thought, I now think I have the solution. What you need is some mechanism that allows for characters to come and go from the ship regularly and without further explanation. My first thought was that they should be passengers, but that stretches credulity quite quickly, as passengers are usually going from one fixed destination to another - they're less likely to keep hopping on and off.
But a better solution, I think, has the remaining characters be agents of "Mister Wolfe" - a semi-legitimate 'businessman' and fixer who employs lots of agents for lots of work, some of it legitimate. For various reasons, his agents would have wide latitude in how they carry out his instructions - they have a job to do, but it's not all-consuming to the exclusion of everything else.
And so the PCs would be split into two groups: some would be formal members of the crew with a specific designated role (excluding the Captain - see below), and some would be agents of Mister Wolfe.
The boat itself would be half owned by Mister Wolfe, with whichever of his agents are present speaking on his behalf, and half owned by the crew (again, excluding the captain). This will give all players present an equal say in what the boat does, where it goes, and if they deviate from their stated agenda.
The Captain is an exception to all of this. That role would be reserved as an NPC, and would have no ownership of the boat either in his own right or on behalf of Mister Wolfe. This has three effects: it means that the tenor of the game doesn't dramatically shift between those occasions when the captain's player is present versus those when he is not; it allows those players who are present to determine the actions of the captain by virtue of their authority over him; and it eliminates any perceived heirarchy amongst the PCs.
And that would seem to be that. The only remaining questions become: when to kick this off, and whether to keep back some of the pre-generated episodes for use with this campaign rather than using them all for "Firefly: the Lost Episodes"?