@bogden I love this idea, especially if the rewards scaled up with more players getting involved. I've got a couple of coworkers who are more likely to hop in if it were a 'friendly' coop where we all worked together. There could also be rate-limiting tied to account, so it really would be in the interest of the community to get more players involved in the season.
A peace-nik hippy flowers love-in commune definitely wouldn't be appealing to everyone, so just cycling in the coop season periodically would be the way to go, then the short knives could come back out in to appease the blood lust of the top tier players.