Enough people willing to play the parts
See concepts of mix networks: As a getting started mixnet scenario you can use:
Just have people send messages back and forth at different times to get the network in a “running state” with a clear “baseline” of observations.
Now ask the observers to focus on three senders to determine who gets whose message. And what else seems noteworthy. Play with mixnet parameters.
The challenge: build a simulation for understanding I2P.