No art for this, I just had a random idea ...
What if, as part of an area wide campaign, you took a sign in registry of all the players who wanted to play in one grand campaign.
You then create one list of random encounters drawn up for all the GMs to use at each level of the overall map.
Everyone makes up first level character. All seems normal.
Each session you rotate GMs, with each using the random table for that level, as well as running a homebrew adventure of their own devising for that level. Neither the GMs nor the players know who will be running/ playing what until you meet up that week.
Every time a character is killed, that player is removed from the event.
As players are removed you reorder the groups, to fill in gaps.
The campaign ends when the characters have survived a fixed number of sessions, or you are down to one group of six or fewer.
When the campaign ends, the final test is to send those player characters through a high level dungeon.
I think this would be awesome!!!! Something you would stream for posterity.
Game design / event thought of the day...