I don't think the word "dead" is appropriate... "mature" seems more like it to me, at least with the development build. I get the impression that Vincent did not want Cog to become bloated with too much stuff (like iTunes).
I agree that a new release based on the nightly would be good for newcomers, but I also understand the effort involved in actively maintaining software and doing releases. Vincent clearly doesn't have time or interest in further releases of Cog, but he has made the source available. I suppose the community here could do a fork, but I worry about a pile-on of new features and the resulting bugs that would arise. As it stands now, the nightly does exactly what I want to my satisfaction.