Is Echo the only map with a "scenario system"? As far as I can see, Echo is the only map with a scenario system, but it seems strange that only 1 scenario uses this option and the rules mention that it can use 4 or 6 slots in the "scenario system", but only the 4 slot is used on Echo map.
I believe the rules state that you can create your own objectives as well, so my group has been considering different things.
Probably the best idea is sector control. The additional objective is to take over the entire map or maybe more than the opposing team if you set a time limit. You would use the scenario meter to announce that you're taking over the sector you are currently in. We haven't tried it yet, but I think it would be fun.