I had asked this at some time, too, because a comm sounded like a good idea to me, too. But some people didn't want it back then, so I'm fine with it. There definitiely are downsides to doing it in a comm which I can't deny, particularly not after various similar experiences as a mod (and the last remaining mod of a comm, too): comms tend to get more anonymous more easily, and might attract more people much quicker, which would take the personal feeling out of this challenge. I'm participating since over two years now and I must say this holds a special charm no community can match. Then, a community always needs some people in charge and being responsible - who end up with doing most of the work, while other volunteers just dwindle away, or don't feel compelled to join in with the hosting in the first place as everybody seems so well taken cared for anyway. Eventually, only a couple of people will remain who do the work, and finally, two or even just one will remain, get frustrated at having to do everything on their own, and eventually stop. Also, there are various similiar communities already out there, so there really isn't a point in just doing another one.
I can't speak for anybody else, of course, but personally, I don't think I'd continue to participate if this was a comm. I tried a couple of writing comms, but it remained always too anonymous for me as I'm not a person to interact and participate socially much, and get quickly isolated, or not integrated in the first place. WED is a refreshing alternative.