Valve recently announced that they would be releasing downloadable content for Left 4 Dead this Spring. One of the new arrivals in the update will be the much-awaited L4D support in the Source SDK, whilst another is the interesting mention of a Survival game mode, "where up to 4 players set records for the longest time surviving hordes of Zombies on over 12 maps". This got me thinking of the possible gameplay changes that could take place for this mode, so here are some of the ones I hope Valve will make (and the ones I'd like to mod in if they don't).
Non-linear, dynamic maps
Rather than getting from A to B like in conventional L4D maps, we will only have the sole primary objective of defending ourselves. This means we are going to be spending a lot of time in a single well-fortified location as this is the best defensive strategy. To prevent this 'fort' from becoming too familiar and stale, it should gradually deteriorate as the hordes attack (blocked exits being broken through, lights diminishing, doors being smashed in, etc.), forcing the survivors to find somewhere safer. This should be based around an element of choice, with multiple escape routes from each area leading into various other 'forts' that the survivors can hold up in.
Maps should allow the players to move find their own way around a large playing field such as a city block or woodland area. Starting positions could be random to force players into decision-making and forming strategies from the very start. This ongoing changing of the maps would help keep them seem more varied and different each time they are played.
Helicopter item drops
I envisage a 'No Mercy' situation where a helicopter pilot is circling nearby but is unable to land to rescue the survivors. The crew could have a supply of items (ammo, first aid kits, pain pills) which they could drop in crates for the survivors to grab (in exposed, open areas of course). The items would become increasingly more valuable as the well-being of the survivors gradually dwindles.
For an extra layer of complexity, the crate might take a short time to open (something like diffusing the bomb in Counter-Strike) so the survivors may prefer to drag it to a safe location before doing so.
If the above helicopter system was implemented, what might determine when and where it performs a drop? A simple timer/random system might suffice which could be controlled entirely by the AI Director, and/or it could be determined by the actions of the survivors. Scavenging empty buildings might result in finding the odd flare which could be used to request supplies, perhaps by launching them from mounted flare guns at pre-determined locations (which could again be randomized by the Director to keep the survivors on their toes).
The infected hordes could attack in large waves which could be counted and available for the players to see. This would give a sense of progress and would surely also determine the difficulty.
I may add to this list in the future. Let me know what you think!
...Especially if you work at Valve.