I believe that's 400 people who told Peter that they would be possibly interested in contributing something back when he first floated the idea. I was one of those 400, but when the time came I didn't have a subject lined up that I felt was suitable for the format. I think that's why starting something like this is much harder than sustaining it. In the next year I might come up with two or three things suitable for the journal and put them aside until I have time to develop them into an article, but coming up with something to fit a deadline is much more difficult. Coming up with a topic for an inaugural issue that will presumably set the tone for the publication is even more daunting.