Ars Magica did this best, I believe. In Ars Magica, all players had one Magus character (basically, the most powerful humans around, when they get a bit of experience), and a Companion characters (rather heroic and exceptional humans that are friends of the Magi). They all lived together in an arrangement called Covenant (which is as much an agreement of cooperation as much as it is a physical location such as a fortress, a built-up cave, a fake monastery, or a wizard's tower) with 10-100 Grogs ("supporting cast", like guards, cooks, hunters etc.) that would be "common property", with each player creating several of them to help with the process.

Magi mostly don't like adventuring. The reason is, they are primarily interested in developing their magical Arts, and one can't do it through Experience - you have to bury your nose in a book or your hands in your laboratory for seasons on end to get a new insight. However, from time to time, they must: local peasantry get ideas about "exorcising those demons from our midst", the fairies make a new hare-brained scheme, a lordling you have good relations with comes asking for favours, or there's the yearly harvest of magic mushrooms in a nearby forest that is contested with a rival Covenant. When they do go out, they don't all go together: maybe two or three Magi go forth, the other players will grab Companions, or several of the more important Grogs as a group, so that in each adventure the troupe composition changes.

Just like Brian S says, storytellers change as they get ideas. Also, different people can be specialised for different type of content. In our campaigns (of more than a decade ago) I was usually in charge of Faerie or Infernal stories, while my friend was more interested in politics and intrigue. You can also have a "grand arc" that only one or two people know about, that threads its way through various adventures, with the person-in-charge sending notes to the current storyteller about necessary clues that need to be embedded in the current story (like overrides).

Ars Magica did this best, I believe. In Ars Magica, all players had one Magus character (basically, the most powerful humans around, when they get a bit of experience), and a Companion characters (rather heroic and exceptional humans that are friends of the Magi). They all lived together in an arrangement called Covenant (which is as much an agreement of cooperation as much as it is a physical location such as a fortress, a built-up cave, a fake monastery, or a wizard's tower) with 10-100 Grogs ("supporting cast", like guards, cooks, hunters etc.) that would be "common property", with each player creating several of them to help with the process.

Magi mostly don't like adventuring. The reason is, they are primarily interested in developing their magical Arts, and one can't do it through Experience - you have to bury your nose in a book or your hands in your laboratory for seasons on end to get a new insight. However, from time to time, they must: local peasantry get ideas about "exorcising those demons from our midst", the fairies make a new hare-brained scheme, a lordling you have good relations with comes asking for favours, or there's the yearly harvest of magic mushrooms in a nearby forest that is contested with a rival Covenant. When they do go out, they don't all go together: maybe two or three Magi go forth, the other players will grab Companions, or several of the more important Grogs as a group, so that in each adventure the troupe composition changes.

For example, in one story, the Fire Blasting Guy and the Revels-in-Conflicts wizard are off to exterminate a goblin infestation in a local brewery, together with Mr. Broadsword and Tracking Girl and five escort. In the next adventure, half a year later, Master Enchanter, Revels-in-Conflicts wizard and Look-The-Normal-People-Are-So-Much-Fun negotiator mage are making an expedition to the regional enchanted item competition, taking their Captain of Guard, Mr. Broadsword, the Cook, the Weird Guy with Voodoo Dolls, the Spy Master, and ten assorted guardsmen.

Just like Brian S says, storytellers change as they get ideas. Also, different people can be specialised for different type of content. In our campaigns (of more than a decade ago) I was usually in charge of Faerie or Infernal stories, while my friend was more interested in politics and intrigue. You can also have a "grand arc" that only one or two people know about, that threads its way through various adventures, with the person-in-charge sending notes to the current storyteller about necessary clues that need to be embedded in the current story (like overrides).