I say we keep the current damage system, but allow assists to detract from the "kill" value of target, while counting as partial kills for those who got an assist.
Example:
Pilots A, B, and C shoot down pilot X. Pilot A did the majority of the damage, so he is awarded 1 "kill" point. However, pilots B and C assisted, so they are each awarded .2 kill points each. These could also be subtracted from pilot A, so he ends up with .6 kill points.
This awards all players who contributed to a kill.
The only downside I can see to it is players who are good shots rolling around tagging everyone they encounter once, allowing others to finish the kills, getting .2 points every time they do it. While the average player wouldn't be able to benefit from this, a good pilot could game this to increase Kills/Time, Kills/Deaths, and Kill Points quite easily.