We use the clan format as a master players list of Extinction Shooters. We play together a lot in Extinction but currently get no clan XP for that... Sometiumes a few of us mosey into MP to play and earn there so it works out.
IW really coulda put some more thought into Extinction, well actually not really. They could have copied BLOP2 in a few ways and give us Extinction Challenges every week that would have helped earn some CXP.
-most cryp kills
-most hives destroyed
We could earn more for playing Extinction with fellow clanners instead of randoms. They could even run these "mini" Extinction events during the off-week of clanwars so even if your clan is not all that good or simply doesn't stand a chance in CW's you (we) would still have the chance to level up our clans!