This is a special game mode that I had an idea for the other day and thought I might suggest it to see if you could perhaps add it ^^.

Starting:
The teams get split up Red and Blue like normal, though the character choices are as follows:
-Blue:
--Engineer
--Volt Master
--Combat Medic
--Reanimator
--Sub-Classes:
---Sniper
---Scout-Bot
-Red:
--Advanced Infantry
--Assassin
--Demolition Droid
--Mech Knight
--Sub-Classes
---Hacker
---Zee-Warrior

The blue team spawns nearly out in the open, what they do is since they are all support classes, is build a base to defend themselves, the Red team spawns out in a box with a small wall that blocks them from leaving, only Red team members can leave/enter the blue base, the blue team has to stay in there. The wall blocking of Red team will open up in 15-30 seconds(Idk what time it should be), giving the blue team time to setup and get ready.

Goal:
The Blue team doesn't respawn when killed, though any obj's/mob's they have made stay on the field(So if they die as an engineer they weren't useless). The red team can respawn as many times as they want, and if the Blue team is all dead Red team wins. Though there is a time-limit, and if the Red Team dosen't kill all the blue team by then, they lose.

Other:
Kills and Deaths would be the score that shows u[p for each individual red team member, though for Blue Team, it would also show how many minutes:seconds they've lived(Whoever has the most is at top, if tied then looks at kills). I just think this is would be a really fun and team-oriented game mode instead of the just-by-yourself-vibe.

.....

Bad idea simply based on most people will not follow simple tasks involving teamwork, decent idea though, potentially could work in an attack/defend scenario ala team fortress, 1 team defends a point for X minutes, other team tries to take it

Proelium 2 is practically all "Team Fortress".

Yeah, but there is no real mode for it, when I was making this I was thinking of Horde mode from Gears of War 2, but yeah an attack/defend mode like Insane said would nearly be the same and work great aswell.

EDIT:
And to fix the team members being dumb, this could be a clan only type of mode, so if some clan members are slackin off or being a holes you could boot them. Cause this is a very team oriented mode.

I know this entire game was based on the class-combat of tf(2) so thats why I referred to it