This is something I've been wishing to see in an FPS for a long time. Basically, to make the relatively long post ahead short, I propose a "Surprise Attack" Conquest game mode in which the attacking side are assaulting a facility and catches its defenders unaware. Said defenders have to make contact with the attackers and request reinforcements, which are then sent in from off-map. The attackers would therefore benefit greatly from stealth and could gain a great advantage from staying hidden for a prolonged time.
The game mode in more detail:
Patrol/Recon Phase: Attackers have recon/vanguard units (I'm thinking scouts here, not "omglol 1337!!11 zpezop"

, and defenders have patrols and sentries. For this purpose, players are allowed to spawn with light infantry classes and are given some light vehicles. Their objective of the defenders at this point is to patrol the area and stand watch at the bases, trying to make contact with the enemy so that they can alert Command and request reinforcements. When a certain condition is met (a defending player successfully spotting an enemy, a kill being made by either side, etc.), the Mobilization phase starts. Until then, Attackers can try to prepare the battlefield by laying mines, gather Intel, etc. There could also be a system in place that rewards them for successfully conducting recon operations while staying hidden (for example, the attacking team could get points or tickets when spotting enemies and facilities without said enemies being alerted to their presence).
Mobilization Phase: Once the defenders confirm the presence of hostiles in the combat area, they radio for reinforcements (the rest of the vehicles and infantry classes their side is issued for the map), which are then mobilized and deployed. The time period between the alarm and the arrival of reinforcements is known as the Mobilization Period. I suppose the facility would have a garrison on-site, though, so some infantry and maybe some vehicles should be unlocked at the onset of the Mobilization phase.
Combat Phase: Eventually, reinforcements arrive (all infantry classes are unlocked and can be requested and all vehicles spawn) and the real fight is on.
Some other possibilities:
- I'm unsure how attacking vehicles would appear. You could have a system where they arrive on the battlefield little by little, a few unlocks at a time, during the Patrol/Recon phase, giving the attackers an edge in firepower during if they manage to stay hidden during this phase.
- There could be certain objectives (bunkers, parked vehicles, entrenchments, CP's, etc.) that attacking recon elements would get points for spotting during the recon phase.
- The defenders could be at a constant ticket drain during the Recon phase. This ticket drain would end come the Mobilization phase, at which point attackers would be on a ticket drain.
I know this sounds very advanced to implement, but I've been surprised before by the PR team (I'm thinking of the Insurgency game mode here), so I thought I'd suggest this. I know this sounds like an advanced game mode to implement, but PR has surprised me before, so I thought I'd throw it out here.