Great idea Wegaman.
I don't see the need to use a multiplier for people in a squad, Mayhem. Squads can just as easily set up missions, and even lead them, to get the bonus points. A lot of squads don't do squat. A lot do. I don't see being a joiner as something that should get bonus points.
Also, I don't know how you would easily define success to award multipliers only if the mission succeeds. What about harassment and decoy missions? Not every mission is to capture a base. As I understand it, medals were awarded in WWII based on individual as well as group performance. "Points" should be awarded similarly.
My opinion is that signing up on a mission gets you a base multiplier. With more points at stake for each kill, each member will be hopefully more interested in accomplishing their objective.
Maybe somehow divvy up all the points acquired during the mission and apply that as a bonus to each member's total?
------------------
Rape, pillage, then burn...