I think a system with six-month seasons is a good idea
The system should go one way only ... the old ISS system was bad because you stopped killing people because they made you lose points
a MMR system similar to Dota2 maybe ... you killed get X points ... you died and you lost X points ... and the more points you have ... the less you will gain by killing someone.
As your score is high, you will receive a "patent" for this between one value and another of MMR