I think putting resources on a new limited-time raid would be a waste, considering that not enough people do the ongoing raids. However, they could put limited-time rewards on existing raids (50 synched and 60) and this would boost participation and possibly invite more people to try it.

For fairness towards new players the rewards should IMO be given in the form of currency, so one could buy any past reward in the future. People should be able to buy one item of their choosing every event, whilst SE makes one new item per event.