Too late to add, but maybe as DLC but have lets say 6 players V.S. 2 turret builders and the builders build and the players use free running and park-our to get through alive...lol just sounded fun ^^
Sounds more like a mod than an actual DLC. I'm pretty sure that SD wants to keep varied objectives in their games and doing a single thing over and over and over isn't their style. Likewise Brink seems built for CtF but this would be more of a mod than anything. I could imagine a DLC including 2 additional skills per class or more universal abilities along with a new maps and locations (including a storyline). I doubt you will see a 5th class or a new gametype as the objectives seems varied on purpose. You could see new features that requires Engineers to repair fixed turrets and allow Operatives to hack/control them however.
Yeah, it does seem more along the lines of a mod. But never the less that would be interesting eh? I'm sure we wont be needing any DLC for awhile though, I'll be busy with my customization for a week or two