First of all I was left unimpressed by the firefight in reach. My idea of a survival mode is to hold up in an area of the map and try to live with limited resources and set lives. Not fly around with jetpacks and rain death with rocket launchers.
So before I start my idea I just wanted to say, make firefight about surviving again.
Now for my idea. I think it would be really cool to have a unique trait for each firefight map. Firefight maps are different than campaign maps and can have more scripted things in them. Here are a few ideas
1 one map can have flood spores that go around infecting the different waves if enemies
2 one map can have an earthquake and some destruction that changes the terrain and such
3 one map can take place in space and feature exclusively space combat
4 one map can have a scarab that is constantly patrolling the battlefield and can’t be destroyed. You simply have to avoid it or temporarily disable it
5 one map can feature air vehicles which no other firefight map has to date
Again these are just examples. DISCUSS