I thought of a similar but somewhat different system where cooperative users of a paying system would point free parking spot when passing by or leaving the spot. This would not ensure the spot to be free upon arrival of a user but it would give an edge and prevent the hassle of dealing with someone who (reasonably) wants the spot you supposedly paid for.

I thought of this while struggling to find a parking spot in Paris. Traffic jams and parking spot searches are great moments to have ideas.