Here's an idea to think about:
A relay race, on the track. Teams can hand off as many times as they want, in any order, wherever on the track they want. Here's the kicker . . . it's a race for survival. A team finishes when they are lapped and ranked ahead of previously lapped teams. To win, the team must lap every other team. There could be a default time limit of like 2-3 hours if there isn't a winner yet and the finish is announced to be in one mile, or not. An open-ended distance would definitely make it interesting.
If it's a serious race, keeping track of where the leader is will be critical and batons will be the key. They'll have gps trackers on them to track the teams' laps. They can even be networked together and illuminate a certain color if they are near the lead, and a different color if close to being lapped.
There would be a ton of strategy. Will teams bet the race will be somewhat shorter and make it a sprint interval workout or work more efficiently? One of the many fun things about this is once the race starts, the strategy will have to change according to other teams. Runners will also need a wide range of speed and endurance. A team may design itself with runners for different roles: "chasers" to take longer shifts and follow a slower pace, and "closers" to pass teams.
The number of teammates per team would make a huge effect, and in fact, this could be variable so faster teams can be handicapped with fewer members. I can see how this could be a great community race, but it could also be an exciting race between professional or national teams.
Thoughts?