I don't agree with the original post suggestions in regards of threat levels or MMR, but leagues used to available in the past for the game, which could give things as display tokens for statues and billboards, but also rewards such as vehicles. Gamersfirst removed it together with the detailed threat levels, in an attempt to make players less competitive, but this made no difference on how players played the missions. Instead it removed the incentive for players to maintain their threat levels and play consistently well, and turned clans into nothing more than glorified friends lists.
As you can probably guess, this later made it easier for players to decide to dethreat as they had nothing to lose, with no work needed to get back to "highest" threat level or caring about their rankings in the leaderboards. If these things would get reimplemented again, they'd of course need to be balanced to the current version of APB, but display tokens and joker tickets seems like appropriate league rewards.