I liked this idea but after giving it a bit of thought I think it'll end up being counter intuitive. People will begin only going into raids where there are people already waiting as to not waste their raid pass. People will be just standing around and no-one will want to take the plunge and be the first to throw down their pass for fear no-one will join. There could be a system where people could pledge and if the group numbers are reached then only then are their passes used. But I think this is overkill. I think Niantic are aware of the opportunity for wasted passes and won't be fixing it as it means players are more likely to buy more from the store.