The other ideas you mentioned are interesting to do once and a while, but I actually think tests take away from the gameplay more than anything. If they are open all the time, it creates a large section of the level which is separated from the rest, and has a completely different style of gameplay. This makes it hard for you to really fit in regular jj2 gamemodes.

However, a test section could work if it is closed off most of the time, and only opened on special occasions (this way you can also give bigger rewards to those who complete it first). It's easy enough to do this with trigger scenery - just make it so the host/admin has to use /trigger.