It's very different from D&D, in mechanics and in play - but In A Wicked Age does a version of this.I wonder if any success has ever been had with a campaign that wasn't strictly linear - where the players had x different character sheets for each level of their character from 1 to x, and on any given session, the GM would run an adventure from any point along a possible timeline, that perhaps took a few sessions to reach resolution, and with the overall effect resembling a kind of mosaic of adventures or stories that perhaps had an interconnecting thread running through them.