I was under the impression the member lists were already optional :o I know we put a lot of emphasis on member lists and sign-up posts being mandatory back in 2012, but that was due to a pretty big amount of new clubs that often times just contained an introduction, which we felt was a tad too little effort to put into the clubs, so it became a thing that was required for the clubs to go through approval. But as the influx of new clubs died down a bit, and as more club owners wanted to be rid of the member lists, it kinda moved from being a mandatory element of the opening post to being more of a recommended element to guide people who were having trouble with getting some content into their opening posts. But yeah, I was fine with no member lists and sign-up posts in clubs, as long as the club owners managed to give the opening posts a bit of content without them that wasn't just a short introduction.
I do see a lot of benefits in members lists though. For one, like you mentioned Wicked, it does feel more like a club. I feel like it kinda gives a sense of unity, and I think that's what distinguishes clubs from simple discussion threads. It also gives way for certain features, like the points system and whatever else creative stuff people can think of and if designed correctly, it can make the opening post look better. But this is all just flavour to the clubs, and a way for owners to mix up the experience, so I don't think that's much of a reason to make it mandatory.
So yeah, in short, I think member lists should be optional, but definitely recommended.