I like the first idea of each participant creating a house with a set-up, everyone who wants to downloading it and working with the creator's story, and then the creator of that house periodically having wildcards that everyone has to abide by. (Obviously, there would need to be a thread where everyone periodically posted what was going on with their sims, so other people could ooh and aah and compare notes.) I don't really like the idea of rotating neighborhoods -- it seems like it would really quickly be too much of a hassle.
Also, I only have the base game + Uni. I've been planning on getting Nightlife, but first I wasn't going to get it until the patch came out, and now I'm waiting for the romancemod and to see if there's a good fix for the furious state, because I don't really like the looks of that. So if there are other people without NL, please speak up! If there aren't, and everyone is going ahead with all this anyway, I might just have to run out to the store real quick.
Oh, and doesn't the official Exchange only keeps the uploaded houses up for about two weeks or something before deleting them if there haven't been a certain number of downloads? I don't know how many people would be doing this, but I don't think that's really conducive to people joining the fun at a later date. I'd be willing to host some of the lots on my website (god knows it needs a real use, as it's currently just sitting there gathering e-dust) after everyone has uploaded to the exchange. This would also be a good way to keep it all easily accessible in case the official site has some of the wonky problems that it has had in the past.
(Also, hi! I've been lurking here for about four months, but only yesterday did I decide to actually post things. I decided it was getting creepy that I knew everyone else and they didn't know me. A bit like peering through the telescope during the daytime, you might say.)