It'll be really simple to complete a usable base system, and provides more than enough opportunity for expansion. If everybody committed now is still committed in a year, you could easily go from a very rudimentary system to a very feature rich expandable megalithic structure.
Wildhoney should change the forum from "TalkPHP Developer Team" to "Ideas".
Something akin to the Wordpress.org Ideas forum, but for PHP in general; basically a place where people can suggest their brainstorms on PHP applications, and see what kind of response there is. Is there a project already in existence performing this task? Is there demand for it? Barrier to entry? Others interested in helping? etc.
Time was the primary issue, we are all doing different things and most didn't have the time for it. I must also admit that I do not know anything about volunteer management (paid employees have to put up with disagreeable decisions) and informal management over the web like this.